Why did the religions happen?

From the beginning God has sent Messengers (e.g., Abraham) to different peoples at different times to teach mankind of God's existence and their relationship to the Creator, as well as give Law for the benefit of humanity. Religions grew from the specific teachings of each respective Messenger. The Holy Books of the world religions each foretold the appearance to come of another Messenger but, because each religion denied that next Messenger, there are now so many religions in the world. From the viewpoint of the Baha'i Faith, God has sent only one continuing religion, with progressive Revelations for an ever-advancing civilization. It is the manmade rituals and doctrine that make the religions appear to be so different but, if investigated, the core teachings of each is identical.