Actually if you think about it wouldn't Islam be going back? In the Old Testament, Koran, Torah, Talmud, whatever you want to call it God was pretty vengeful wasn't he. Musa, Elijah, Job, Noah, Esther, David, Solomon, all have stories of God's vengence against not only their enemies but against themselves. When Isa came around all that changed. Isa said he came not to destroy and condemn but that you may have life and have it more abundantly. When Isa came the rules and God's vengence lightened up. He healed beggars and thieves, and adulters and liars. If you sought him he didn't turn you away. He didn't care he just took care of you. He saved an adulterer from being stoned to death. That person didn't call out to him he just did it. So now you're telling me that Allah is going to follow up this man who today would be considered an ultra liberal with a Therocratic back to hell, fire and brimstone type of prophet. It's almost as saying Allah made a mistake with Isa and he sent Muhammed to fix it. Last time I checked Allah don't make mistakes.