I do believe that there was a Jesus, Mohammed, Budda, Gandhi and Lennon (John). I do not "Believe" in any one more than the other.
(Mohammad, Buddha) Anyway, this is my belief: The Bible says that the "demons believe and tremble." This is because they do not believe IN , trust IN, rely ON, believe ON, etc. Jesus Christ. We may believe there was a man named Jesus, a historical person, a good teacher and example, but many do not believe IN him. He taught that, "He that believes IN ME has everlasting life." What this means is that we believe and trust that what he said he would do he did. He said, “We are going up to Jerusalem, and everything that is written by the prophets about the Son of Man will be fulfilled. 32 He will be delivered over to the Gentiles. They will mock him, insult him and spit on him; 33 they will flog him and kill him. On the third day he will rise again.”(Luke 18)
Why he did this, again this is only my personal belief, why he died was to pay the wages of our sin which is death so we don't have to. So if we trust him, that he did this and it was enough, then he freely grants us eternal life because our sins are paid for. Or if we choose not to accept the free gift, then we choose to pay for our sins ourselves. But to one who has accepted Christ's payment, the penalty is paid in full, their sins are forgiven, forgotten, gone further away than east is from west, which is infinity. They are blotted out, remembered no more, never brought up against them again, thrown in the depths of the sea, paid for by the blood of Christ. And that's not all! To one who has trusted Christ, Christ gives them HIS righteousness (like a robe) in place of their own which is as filthy rags before a holy God as far as salvation is concerned. That's what I believe. I simply believe in Jesus. That's all it takes.