According to St. Augustine,
"That which is called the Christian religion existed among the ancients, and never did not exist from the beginning of the human race until Christ came in the flesh, at which time the true religion, which already existed, began to be called Christianity."
That Augustinian statement at first surprised me especially since St. Augustine is held so highly in Christian circles (and elsewhere as well). However, upon reflection, it makes complete sense. If, in the history of the world, Jesus had been the sole originator of the truth of God, it would be no truth; for truth cannot be originated; it exists.
Truth is Eternal.
When I was at the Khumba Mela (a Hindu happening which is the largest spiritual event in the world) in Haridwar, India, in 1998, I wandered into a tent where the guru (literally one who removes ignorance) was speaking in English. (I don't understand Hindi so an English speaking guru was quite welcome especially since there was also food and refreshments at that ashram.
) Although he was a Hindu, I quickly realized that he was teaching from Lord Jesus' Sermon on the Mount. When some one in the audience questioned why he was teaching from the Sermon on the Mount, he simply replied that Lord Jesus' teachings are among the best anywhere and he could see no reason why not to quote Him along with others.
Truth is Eternal.