For every cycle of the fixed stars (what we call "a year") the moon goes through 12 cycles (approx) which is what we call "the months".
This was the basis of Mesopotamian (Sumerian, Akkadian, Babylonian, Assyrian) number systems rather than 10.
12 is an impressionistic reference to completeness as well as the number of the children of Jacob and the ancestors of the 12 tribes of Israel.
This is the basis for the also impressionistic number of the saved, 144,000 (12 times 12 times 1000)‑ The new Internationally overflowing Israel of the Revelation to St. John the Divine