Many including Muslims assume that Islam was revealed 1,400 years ago. During the time of revelation Islam was a new revelation unlike that of the previous Prophets, but they would be wrong. The holiest Muslim book states otherwise.
Say: We believe in Allah and (in) that which had been revealed to us, and (in) that which was revealed to Ibrahim and Ismail and Ishaq and Yaqoub and the tribes, and (in) that which was given to Musa and Isa, and (in) that which was given to the prophets from their Lord, we do not make any distinction between any of them, and to Him do we submit.
And Abraham said,
No associate has He; and this am I commanded, and I am the first of those who submit.
The previous Prophets are mentioned in the Quran as being those who submit to God. Submission in Arabic also means Islam, and those who submit are called Muslims. Prophets sent by God could not have brought different messages.
IF God is one why would He send Prophets with different messages each time? It is understandable that God sent Prophets time over time to reiterate a message and remind mankind. Over time the divine teachings of the Lord changed.
Hence God sent Prophets to reiterate the same message, to worship the one and only Lord. As mentioned in the Bible,
Hear, O Israel: The Lord our God, the Lord is one.
Jesus answered, “The most important is, Hear, O Israel: The Lord our God, the Lord is one.
and in the Quran
Say He the God is One
One simple message sent many times through different Prophets. God sent the same message through Prophets that were sent for the people of a time. Muhammad was the last Prophet, should we not follow the Prophet sent with a message till the end of time?