Imagine there are two people on a flat piece of paper. These people are two-dimensional, having height and width but no depth; the paper is the extent of their world. Can they see you? No. They can see only what's on the paper (in their world). They have no depth perception. Now pretend you use your finger to touch the paper. Now can they see you? They cannot see all of you, but they can see the tip of your finger, the part that has entered their world.
That is an analogy of our situation with God. God exists outside our dimensions. He can exist outside of time and space as we know it. Therefore, it is difficult to "see" Him. We are like the flat people on the two-dimensional paper. We can't see what's in a third dimension. But in this case, we exist in four dimensions (height, width, depth, time), and God exists beyond that.
So how are we to know such a Being? Just as the "flat people" on the paper could not know about you unless you touched the paper, we cannot detect God unless he reveals himself. He must "touch the paper" of our world. God has to step down in dimensions.
As we study human history, especially religious history, do we find any instances where God "touched the paper" of our world? Consider that God's "finger" has touched our world in a person known as Jesus Christ. Jesus claimed to be God1, said that to see him was to see God2, said that he was the only person who had come directly from God to our world3, and forgave people of their sins, which only God can do.4 Many other passages of the New Testament affirm Jesus' deity.5 He was God who "became flesh and made his dwelling among us."6 He is the "image of the invisible God."7
If we are the "flat people" it makes sense that the multi-dimensional Creator God entered our four-dimensional world by becoming a human being. He revealed himself to us. But why would God do that?
There is a story told of an old farmer who lived by himself in a cabin. Next to his cabin was a barn. One very cold wintery night, birds began to crash into the windows of his warm cabin, trying to escape the deadly cold. So the old man went outside and opened the barn door. It was warm inside the barn. He waved his arms and shouted at the birds to go into the barn, into safety. But they did not understand him.
It was then that the old man wished that he could become one of them. If he could become a bird, then he could lead the other birds into the barn, to avoid death. And at that moment the old farmer understood why Jesus had come. Though the old man could not become a bird, God could become a man. So he did. "For God so loved the world that he sent his one and only Son, that whoever believes in him shall not perish, but have eternal life."8
To find out more about God coming into our world, see this article for a full explanation: Beyond Blind Faith.
(1) John 8:58, 17:3
(2) John 12:45; 14:9
(3) John 3:13
(4) Mark 2:5
(5) John 1:3,4,18; Hebrews 1:1-13; Colossians 1:15-20, 2:9; Philippians 2:6
(6) John 1:14
(7) Colossians 1:15
(8) John 3:16