Abraham was not really an innovator or someone proclaiming an entirely new concept of religious belief.
He was simply the first person in a long time to relate seriously to an old religious outlook which was primary and genuine.
He was a great man in his own terms–a leader of a tribe, a successful man of the world, a conqueror in battle, a fulfilled man in private life, and a thinker who was not subdued by adverse public opinion.
In other words, he was a great leader who fulfilled the same function as in later generations would be attributed to a messiah-the restoration of the ancient system of right relations between man and the Divine.
–Rabbi Adin Steinsaltz
From Biblical Images by Rbbi Adin Steinsaltz