There was no replacement of beliefs in the Old Testament. The same Father spoke in both. Both Testaments are of the very same God.
To fulfill the law was not to replace the law. The law never saved anybody in either the old or the new testament. Faith is what saved people in both. The law was only given to help people understand sin. I believe it's you who needs to do some more studying of the bible.
The Koran was just dictated to Mohammad by God, Therefore there is no seperation in time or thought.
Except it wasn't God, it was a spirit. Mohammad thought it was an evil spirit, but his wife convinced him it was good spirit. This is one time when a Muslim really should have ignored his wife. Mohammad was right the first time.
And Except that it wasn't dictated to Mohammad. Mohammad was illiterate. Mohammad recited and eventually it got written down, but by whom and when I don't think they know.
Therefore there is no separation in time or thought.
But the Koran in one place claims to accept the previous scriptures. And then it contracdicts them. And then it claims that it has no internal contradictions.
Therefore there is a separation in time or thought and then not and then just a jumble of confused and contradictory thought.