Christianity either stands or falls on the person of Jesus.
There is no real question that there was an historical person called Jesus. This was an important thing for me to establish for my personal belief. There are numerous ancient non-Christian references to Jesus (for example, Pliny, Tacitus, Suetonius, Josephus etc. all mentioned Jesus). I won't go into this here, but if it's important for you, you may like to get hold of:
Barnett, P., Is the New Testament History? (Sydney: Hodder & Stoughton, 1986)
On the basis that there is an historical Jesus, the important question becomes whether he was of God or something else.
A noted Christian writer, C.S.Lewis, once said:
"People often say... 'I'm ready to accept Jesus as a great moral teacher, but I don't accept His claim to be God.' That is the one thing we must not say. A man who was merely a man and said the sort of things Jesus said would not be a great moral teacher. He would either be a lunatic - on a level with the man who says he is a poached egg - or else he would be the devil of hell. You must make your choice. Either this man was and is the Son of God: or else a madman or something worse."
The problem is that Jesus said he was God. This means that, if he was not God, he was either a liar or a lunatic. In my view, it is improper on the one hand to say Jesus was a good man and then on the other to say that he was either a liar or mad. As a matter of logic Jesus needs to be either accepted or rejected - a middle ground is not available.
So, was Jesus a liar?