It is incomprehensible that God should exist, and it is incomprehensible that He should not exist; that the soul should be joined to the body, and that we should have no soul; that the world should be created, and that it should not be created.

—Blaise Pascal, Pensees

One night I sat up until two o'clock listening to two friends recount their difficulties in relating to God. Judy described her many attempts to "break through" to God—attempts that had produced nothing but a sense of cold, disapproving silence. Stanley told of his lifelong struggle to feel that he mattered, that God cared.

I knew these two friends well, and it seemed obvious to me they were projecting their own family dynamics onto God. Judy had lost her mother at an early age. Although her father valiantly worked to raise three daughters in a stable home, he had never conveyed much warmth. She viewed him more as a schoolteacher, or an athletic coach, judging her performance and always raising the bar one notch higher.

Stanley came from a large, lively family of seven which had no lack of warmth or energy. Still, as the fourth child, and a twin at that, he had the persistent, nagging sense of being overlooked. Teachers in school invariably compared him to his older siblings. His father never quite mastered the skill of telling him apart from his twin, even though the two were not identical. "I sometimes think if I disappeared from my family, it would take a week or two for anyone to notice," he said with a wry smile.

In our conversation, I described the God I had come to know, a personality very different from their projections, and also very different from my childhood pictures of God. That evening reminded me that everyone has an image of God distorted in some way—we must, of course, since God transcends our capacities to imagine him. Our experiences of family and church combine with stray hints from literature and movies (The Scarlet Letter, "Sinners in the Hand of an Angry God") to determine what image of God we carry around. Judy told me that a single phrase used at her mother's funeral, "God took her to be with him," formed a block in her relationship with God that she has yet to overcome.

How, then, do we know the true God? If Judy and Stanley had been de scribing one of my friends, and I sensed they had an unfair impression, I could introduce them to my friend to help them form a different, truer picture. (In fact, something very similar had happened: Judy had very negative impressions of Stanley until I insisted she must get to know him better.) How can I do that with God? Knowing an invisible God has little in common with knowing a living, breathing person. Or does it?

To answer that question, I must first digress to explore how we know anything. The process of knowing takes place in the brain, the most isolated part of the human body. Ironically, simple animals, such as amoebae, experience reality more directly than we do. An amoeba wanders into a morsel of food and engulfs it; it touches a toxic chemical and shrinks back in alarm. The amoeba has no processing center, like a brain, to interpret and mediate what it encounters: all of the animal experiences the reality before it. "Higher" animals, and especially we humans, experience reality more indirectly, through the brain—which, though isolated, has amazing powers of reflection and projection.

A thick sheath of bone protects this seat of knowledge from any contact with the outside world. The brain never "sees": if a surgeon exposed it to light for an extended time, it would see nothing, and likely be irreparably harmed. The brain never "hears": so cushioned is it against shock that brain cells can detect only the loudest sounds, like a jet airplane, which cause them to vibrate. The brain has no touch or pain cells. A brain surgeon need only anesthetize for the procedure of cutting through the skull; once inside, he can move or cut brain tissue at will. Its temperature varies no more than a few degrees; it never feels heat or cold. It almost never sustains a mechanical force; encountering one, it would quickly lapse into unconsciousness.

Because of the brain's isolation, everything that forms my knowledge of the world reduces down to a sequence of electrical signals, like the dots and dashes of Morse code, reporting in from millions of nerve sensors. Think of the voice that comes to you over the telephone. Someone on the other end speaks, and electronic equipment changes those sound waves into electrical signals which pass through relay stations to be reassembled on your end as vibrating sound waves. If the caller uses a cell phone, the sound is translated into packets of digital code and broadcast through the air, like a radio transmission, before entering your telephone receiver. Yet you "hear" your mother's voice.

My isolated brain must trust signals much like those digital codes in order to perceive the world. The doorbell rings and I get up to answer it. Tom, the UPS driver, has a package for me. I greet him, sign for the package, and return to my desk. It would take a computer programmer to appreciate fully the miracle involved in my recognizing Tom. Sound receptor cells in my ear first detected the frequency of my doorbell, approximately an octave above the musical "middle C," and then interpreted the much more variable pitch of Tom's bass voice. Computer software now has the ability to recognize individual voiceprints, and even words spoken clearly by a speaker. No computer, however, has yet mastered the much more difficult task of recognizing a human face.

The human eye has 127,000,000 receptor cells, called rods and cones, that report on the shape, texture, and color of Tom's lips, eyes, eyebrows, nose, and hair. They do this effortlessly, comparing the results to a memory bank of all the faces I know, in a fraction of a second. I do not have to stand and consciously assemble all the data corresponding to Tom's face. (In a brain disorder called prosopagnosia, a person loses this ability; even while staring at the closest family member, a person afflicted with this malady cannot recognize the face.)

All the processing of data from the senses—touch, pain, hearing, sight, smell—takes place inside the bony box of skull. Less than one percent of nerve cells gather this information for the brain, and then carry out its orders: playing the drums, cooking a meal, speaking a language, typing this sentence. All other nerve cells remain locked inside my skull, communally processing the data and delegating instructions at lightning speed. The brain's total number of connections rivals the quantity of stars and galaxies in the universe.

Naturally errors, or "illusions," creep in, and in fact every person who has ever lived has a different perception of the world. A color-blind person does not notice Tom's blue eyes; a deaf person does not know the pitch of his voice. Yet so resourceful is the brain that a great composer, like Beethoven, can "hear" an entire symphony in his head even when totally deaf. Or, a deaf and blind person, such as Helen Keller, can assemble a "picture" of the world that gives striking new insight to those of us more sensorially gifted.

I mention this anatomical background to illustrate that all our so-called "knowledge" of other people involves an act of faith. I trust what my senses tell me, at the basic information-gathering level and at higher interpretive levels as well. Although my closeted brain has assembled an inner image of each person I have met, I realize that the image involves a large measure of trust. I trust that Tom is not wearing a mask, and that he indeed works for ups and is not a burglar scouting my house.

I think I know him, but how can I be sure: Perhaps Tom is an identical twin who job-shares with his brother. So many times people have surprised and misled me. I have learned that one of my best friends had a secret life of sexual addiction, that another was abused by her father for 15 years. I thought I "knew" these friends, only to find I was missing vital information about them. All human relationships involve a kind of approximation; it preserves "otherness." We always fall short in knowing another.

Nevertheless, at the most basic level I trust that these friends actually exist as individual persons much like myself. How can I know for sure? The problem of "other minds" poses a major puzzle that has exercised philosophers for many years. I know that I exist, and I think I know my own mind. But how do I know your mind? I believe, by analogy, that when you shut a car door on your finger, something inside your brain happens that closely resembles what I experience when I slam a car door on my own finger. Yet I can never know for sure, because I cannot get inside your mind; I must take your word for it when you tell me how much it hurts. I have learned that other people experience the world differently from the way I do. A concert by the Chicago Symphony Orchestra sends me into rapture; a Phish concert may do the same for you.

How do you know that I exist? You are reading words on a page, but perhaps Philip Yancey is a pseudonym. Perhaps this book is being written by a committee, or by a programmer at Fuller Seminary who cleverly devised software to crank out books of popular theology. If you try to contact me on the Internet, you will never know for sure whether it is I responding, or simply a concocted screen name. To me, I am an I; to you, I am a you, and that distinction introduces a powerful strain of uncertainty.

Admittedly, most people do not go around questioning whether other minds and persons exist. We take it for granted, without giving it much thought. Yet as we encounter other people, every one of us assembles a different composite of that person. Think of the authors of the four Gospels: Matthew, Mark, Luke, and John were each struck by different aspects of Jesus' personality and life. As they reflected on what they knew about him, different words and scenes came to mind. Or consider the disciples; 12 of them followed Jesus around for three years, but what different conclusions Judas and Peter drew about him! Later, a Pharisee named Saul of Tarsus thought he had Jesus figured out, until a personal encounter radically changed his opinion, and altered the direction of his life.

Perhaps what I have learned about the process of knowing other people can shed light on questions about knowing God.

First, I recognize that knowing other minds involves an act of faith, whether I am speaking of other persons or of God. George Berkeley stated the philosophical problem long ago:

It is plain that we cannot know the existence of other spirits [persons], otherwise than by their operations, or the ideas by them excited in us. I perceive certain motions, changes and combinations of ideas, that inform me that there are certain particular agents like myself which accompany them and concur in their production.

In other words, we know other minds indirectly, not directly. I assume you exist, and have an outlook on the world somewhat like mine, but I can never be certain. Alvin Plantinga, a philosopher living 250 years after Berkeley, applies this problem to the question of the existence of God. I cannot be certain of God's existence, he acknowledges; I cannot prove it. Yet I can't be certain of anyone else's existence either. I believe I am not alone in the universe, but because I cannot perceive any other person's mental state, I must accept this belief by analogy—or by faith. In fact, I have as much evidence for believing in God as I do for believing in other people. Although both lie beyond proof, I accept both as a basic, foundational assumption.

In addition, I also recognize that my senses never give me a complete representation of another person. I can learn a lot about you through watching you, listening to you, touching you. Yet there always remains a part of you inaccessible to me, the person inside your body, the real "you." In George Steiner's words, our comprehension "most particularly when it deepens into intimacy, will remain partial, fragmentary, subject to error and to revaluation. But this knowledge does not induce us to presume that the presence before us is one of spectral vacancy or falsehood." I trust that you are really there.

I learn this best from disabled people, who have lost the close connection between mind and body which healthy people enjoy. I had a wonderful friend with cerebral palsy who was mistakenly confined to a home for the mentally retarded for years. Her arms flailed about spastically, she could not walk, and she drooled and made grunting sounds instead of words. Most who met her—tragically, even her own family—assumed she was retarded.

In time, though, professionals recognized that Carolyn had a fine mind locked inside that uncooperative body. She moved to a more appropriate home, attended high school, and then college. Eventually she became a writer. Once, at her college, a friend read a chapel address Carolyn had written. Students sat in total silence and listened to Carolyn's eloquent words as she slumped in a wheelchair onstage beside her friend at the microphone. (She had chosen as her text, "We have this treasure in jars of clay.") All had seen her wheelchair on campus, and some had even made cruel jokes at her expense; few had made the effort to get to know the remarkable mind at work inside Carolyn's twisted body.

Another friend, Don, is currently fighting a degenerative nerve disease like ALS (Lou Gehrig's disease). I knew Don as a rugged outdoorsman who ran a horse ranch and led white-water canoeing expeditions. When I last visited him, though, he sat in a wheelchair. Though he could still talk, the nerves controlling voice and language could not keep up with his mental instructions. He stumbled over words, and the simplest phrases stumped him. He preferred to type his thoughts into a laptop computer which would then speak for him in a weird Darth Vader-type voice. Anyone walking into a room with Don would see a man sitting very still, saying nothing, with a gentle smile at times crossing his face. But the disembodied words that came out of the computer, and the lucid e-mail messages I get from Don to this day, prove that inside that placid exterior, a lively and witty mind endures.

I am very thankful that modern technology allows both Don and Carolyn to communicate even when they lose the bodily functions that allow speech. Stephen Hawking, one of the world's most brilliant scientists, can move only one finger of one hand, and yet through the same software Don uses, Hawking can address scientific gatherings (an Englishman, he says he dislikes the program's American accent). I read a book "written" by a Frenchman who could only blink his left eyelid; a nurse would run her finger across the alphabet on a poster board until he blinked at the letter he wanted, then begin all over again until he signaled the next letter of the word. Yet even if these people lost all ability to communicate, through total paralysis or a stroke-induced aphasia, I would assume that somewhere inside them the mind would live on. It would be truly tragic if they reached such a point of decline that no one else could access their minds, for we must inevitably rely on other people's bodies to convey to us their minds.

Which brings up an interesting theological question. Since God has no body, how can we perceive him? How can we communicate with him? Could it be that we possess the capacity for "direct" knowledge of God, meaning without reliance on the body and its senses? If so, our knowledge of God would operate at a different level than our knowledge of other persons. We would not need for God to appear be fore us in material form. And God, a spirit, could use a kind of direct intuition in communicating with us. Different rules would apply to communication with God, for God doesn't "need" our bodies to access our minds. As Tennyson wrote in a poem, "Closer is he than breathing, and nearer than hands and feet."

Every animal on earth has a set of correspondences with the environment around it, and some of those correspondences far exceed ours. Humans can perceive only 30 percent of the range of the sun's light and 1/70th of the spectrum of electromagnetic energy. Many animals exceed our abilities. Bats detect insects by sonar; pigeons navigate by magnetic fields; bloodhounds perceive a world of smell unavailable to us. Perhaps the spiritual or "unseen" world requires an inbuilt set of correspondences activated only through some sort of spiritual quickening. "No one can see the kingdom of God without being born from above," said Jesus. "The man without the Spirit does not accept the things that come from the Spirit of God, for they are foolishness to him, and he cannot understand them, because they are spiritually discerned," said Paul. Both expressions point to a different level of correspondence available only to a person spiritually alive.

"Now this is eternal life," said Jesus: "that they may know you, the only true God, and Jesus Christ, whom you have sent." The highest correspondence, reserved only for the creature made in God's image, even organic death is powerless to arrest. No material event, not even death, Paul insists in Romans 8, can separate us from God's love; God keeps alive that which he loves.

As the key to access the unseen world, the Bible presents faith, which Hebrews defines as "being sure of what we hope for and certain of what we do not see." Jesus clearly hinted that after his death, something new would happen, a new way of knowing: not the normal process of an isolated brain forming pictures of reality, but an internal and direct path of knowledge. "When the Counselor comes, whom I will send to you from the Father, the Spirit of truth who goes out from the Father, he will testify about me," Jesus said. "But when he, the Spirit of truth, comes, he will guide you into all truth. … He will bring glory to me by taking from what is mine and making it known to you."

According to the Bible, the greatest distinction between human beings is not based on race, intelligence, income, or talent. It is a distinction based on correspondence with the unseen world. The "children of light" have that correspondence; the "children of darkness" do not. One day our correspondence with that world will be complete, not partial. As John said, "Dear friends, now we are children of God, and what we will be has not yet been made known. But we know that when he appears, we shall be like him, for we shall see him as he is."

This is part 1 of a two-part article.

Philip Yancey is the author of many books, including most recently The Bible Jesus Read (Zondervan). This essay is adapted from his forthcoming book, Reaching for the Invisible God, which will be published by Zondervan in the fall.

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