God in His mercy had sent messengers to convey His message, to different peoples, in different times. Each prophet came with guidance and miracles that were relevant for his time, and for his people, but the message was the same: That there is only one God, and worship is for him alone. This "Islam" was the religion brought by all the prophets of God. Islam was the religion of Adam, Noah, Abraham, Moses and Jesus (peace be upon them all). God has in His Grace, addressed this issue to man in His final revelation, the Noble Quran.
