A variety of reasons, I think. It starts with my parents. I grew up in a Christian home. My dad was a pastor. I was taught the Christian faith.
But at some point every Christian-raised child has to come to a point where the faith of his parents either becomes his own or is rejected. As I progressed through my teen years, questions regarding truth and reality of Christianity arose in my mind. So I started asking questions, and I sought answers from my parents, pastors, professors, and authors.
For me, the core issue was whether the Bible was reliable or not. If it is, all is (more or less) explained. If it isn’t, then the Christian faith collapses.
Ultimately, my foundation is the reliability of the Gospels. I found that the four Gospels—Matthew, Mark, Luke, and John—when tested, are historically reliable documents. There are certain tests that historians apply to historical documents to reach conclusions about their reliability. The Gospels ace those tests.
Trusting the Gospels’ integrity, then, I learn from them Jesus' teaching about himself, about God, about humanity, about sin and salvation. I also discover his opinion of the Old Testament. The truth of the entire Scripture for me is verified in the assertions of Jesus of Nazareth as recorded in the Gospels.
Now tis true I could regard Jesus as a loony whose loony teachings and claims are accurately recorded in Matthew, Mark, Luke, and John. But the full portrait of Jesus in the Gospels does not paint a picture of an insane man. He seems self-possessed.
Why do I believe? I’ve given two reasons so far: my upbringing and the historical reliability of the Gospels. I offer one more.
There’s also the witness of countless other Christians—in the Scriptures, throughout history, throughout the world today, and in my own life. Many of each of these witnesses not only believe, but they claim to know Jesus Christ, to talk with him and be led by him. They claim friendship with him that brings joy and peace and that sustains them through troubles.
Not only do they know Christ, but many of them have been transformed by him, changed for the better. I personally think there’s no greater miracle than a changed heart, and one that’s changed for the better. It seems Jesus does this far more than anyone or anything else does.
Those are some reasons why I believe.