In all of humanity, God has not left us alone. Abraham the first major prophet is the Ancestor of all the others, in a human genetic sense. Each prophet came to a different part of the world and a different period. For example, Buddha Krishna, and Zoroaster are not commonly considered part of the chain but they are. In the Judea-Christian chain, Moses followed Abraham and then Jesus followed Moses. After Jesus came Mohamed and then Baha'u'llah.
Each Prophet has the purpose of educating humanity and each prophet brings us closer to a world where we recognize that all of humanity is one and that God is One. There is no difference between the religions, only custom and the people who have corrupted the religions for personal power after the appearance of the Holy ones from God.
Consider this, in all the religions, the Ten Commandments stand in one way or another. They all follow a common belief thread.
