Christianity isn’t true just because the Bible says it’s true. Christianity is true because an event occurred.
True, we wouldn’t know much about Christianity if the reports of the Resurrection had never been written, but the Resurrection preceded the reports of it.
Paul was a Christian before he wrote a word of the New Testament. So was Matthew, John, James, Peter, etc. Why? Because they had witnessed the resurrected Jesus.
Contrary to what some skeptics may think, the New Testament writers didn’t create the Resurrection—the Resurrection created the New Testament writers.
In other words, the New Testament documents didn’t give us the Resurrection. The Resurrection gave us the New Testament documents! There would be no New Testament unless the Resurrection had occurred.