When we look at the moon from the Earth, we always see the same light spots, dark spots, and shapes. It never changes. There could be two possible reasons for this:
-- The moon is a flat disk with some markings on it, and one side of it always faces the Earth.
-- The moon is a round ball with some markings on it, and one side of it always faces the Earth.
Either way, since the same side always faces the Earth, the only way that can happen is if the moon's revolution around the Earth and rotation on its axis both take EXACTLY the same length of time.
Even if they were only one second different, then we would see the moon's whole surface over a long period of time. But we don't. So the moon's rotation and revolution must be EXACTLY locked to the same period of time.
