For me, one of the strongest arguments for the truthfulness of Christianity is the martyrdom of Jesus disciples. Not the ones that came along later and believed previous peoples’ accounts, but the ones that were physically with Jesus and wrote the first accounts. They didn’t believe in someone else’s second hand testimony about Jesus, they themselves hung out with him while he was alive, saw him die by crucifixion, and then hung out with him again after he rose from the dead.
Of key importance was the fact that they were prepared to die for their testimony that Jesus had risen from the dead. I cannot see any other reason for them to die for their testimony other than that they were fully and deeply convinced of it and its importance. I cannot see how they could be deluded, or that they were mistaken. They saw Jesus, all of them together, touched him, eat with him, and talked with him, many times, over many days. I am convinced that there testimony is true. Its hard to imagine any stronger evidence than that which we have.
Just watched this video were piper says why he thinks Christianity is true:
1) Historical reasons. There are sound historical arguments for the existence, death and resurrection of Jesus and the acts of his disciples.
2) Presuppositional reasons – without God as an assumption, all of our reasoning processes are not well grounded (ie we have no reason to trust them). (He didn’t mention it but I guess he is thinking of the ability to know what reality is, to understand the universe, etc).
3) Credibility of eye witnesses. Paul is telling us that he met the risen Lord Jesus. We have his testimony. Is he mad? Deceived? Deceiving me? As he reads them the witnesses sound truthful.
4) The Credibility of Jesus as portrayed in the bible. The portrayal of Jesus is self authenticating. I heard someone say once that if Jesus was made up then the guy that made him up is worthy of our worship for being such a genius.
Only thing I would add, which probably comes under Pipers presuppositional heading, is foundational reasons. God provides the foundation for justice, truth, morality, physical origins, purpose, personhood, consciousness, love etc. Without a personal (or more accurately persons ie the trinity) these things deflate or even evaporate.
Heard Keller recently also talk on the subject of being convinced about Jesus.
The question is put to him: Are you res convinced today that Christianity is true, personally, you, are you?
He replies : More so than ever.
When asked later why he had so much peace he talked about how, while ill with cancer, he read a book by N T Write (a world class bible scholar) “The Resurrection of the Son of God”. He says this took his conviction to another level because of the rigorous and intellectually strong arguments in it for the resurrection of Jesus from the dead. I have the book but its size is rather daunting and I’ve not read it yet.