1. The New Testament writers were very careful and accurate, checking their sources and getting eye witness accounts. Luke visited people who lived with Jesus, Luke 1:1-4. John was an eye witness gospel writer, John 19:35. Paul listed the witnesses of the resurrection, 1 Corinthians 15:4-8.
2.Jesus fulfilled hundreds of prophecies made over thousands of years. It would be impossible for just any man to have fulfilled them. Who could invent Jesus and His birth, life, ministry, death and resurrection which were foretold?
3. Outside sources support the Bible, Josephus an historian recorded facts about Jesus life. "History of the Jews" AD90. Thallus, a non Christian mentions the darkness over Rome at the time of the crucifixion writing in AD 52. Seutonius, official historian of the Ceasars, spoke of the Jewish disapproval of the followers of Christ who were then expelled from Rome.
4. Archaeological evidence, the facts, places, names of people. Historical evidence speaks for itself.