I could point to evidence from nature. Why is there something rather than nothing? And why is this something beautifully arranged, as if it was designed? We live on the razor’s edge in a universe that is finely tuned for life. If the Earth orbited much closer to the sun we would burn up; if it inched farther away we would freeze. If gravity had been stronger or weaker than one part in 1040 (that is a ten with forty zeroes behind it), then life-sustaining stars such as our sun would not exist.
Or think small. Every time you scratch your skin, about ten skin cells flake off and become stuck beneath your fingernail. Each of these cells contains your entire genetic code, which if stretched out would fill three hundred Encyclopedia Britannicas (remember them?). Somehow each cell knows to read only that part of the code that pertains to its place in the body, and somehow for most of us this voluminous code is mostly spelled correctly. Just one typo in this three hundred book set—one wrong letter in the wrong place—may cause a debilitating disease or deformity.
But though “the heavens declare the glory of God” (Psalm 19:1), the evidence from nature is not the main reason why you believe in God. Here is how you can know for certain that God exists: You just do.
How is that persuasive?
Because you know that you do.
The Apostle Paul declares that you, along with everyone else, know that God exists. He writes, “For since the creation of the world God’s invisible qualities—his eternal power and divine nature—have been clearly seen, being understood from what has been made, so that men are without excuse.” Paul says that God has made his existence “plain” to everyone, so no one can stand before God and say they honestly didn’t know about Him (Romans 1:19-20). Many may plead ignorance, but they don’t have an excuse that God will accept. He knows they know better (Despite Doubt: Embracing a Confident Faith, p. 49).