If I claim to be God but don't prove it, then either:
-I am a deceiver
-I am lunatic, or crazy
But:
- Jesus spoke the truth so that no one could replied back at the truths he claimed, because it was the truth. He was not bringing the attention to him just to get attention like an attention-craver starlet would do, he was clearly saying that what God wants is people's heart and not their outward good-deeds. How can that be not true. we can see it in our relationship with someone, I don't want you to just show you like me I want you to really love me, but I can't force you. His point was "Love your neighbour like yourself" and "Love God with all your heart and all your mind". To me it sounds very true. and in accordance with my experience of life. The main point of life, at least from what i see, is love (well I am not a lovey-doey kind of guy, but still in the ideal it's love, sincere and deep love)
-Also, he performed miracles not for his own glory but for specific events like healing, walking on water, multiplication of bread and fishes..., so he could clearly show that he was who he was saying he was. But obviously a lot of people still didn't believe his claims as the Messiah.
-He clearly accomplished prophesies (you can always argue that it was made up by the disciples or the writers of those accounts).
-He knew he was going to die and he knew he had to die for the sake of humanity and God's promises.
He also resurrected, and the disciples (+ 500 other people) were witnesses to that when Jesus visited them.
And then the disciples started to "preach" in Israel first and then to the gentiles.
If you really want to know what Jesus is all about I guess you can find lots of books on Amazon typing "Jesus History" or something like that.