Others add even a fourth mitzvah: ritual slaughtering, as it says (Exodus 29:38), “And this is what you shall offer upon the altar.” Rashi (Menachot 29a) explains that concerning all these mitzvot, Moses was not able to figure out how to do the mitzvah properly until Hashem showed him.
The Mishnah (Rosh Hashana 24a) tells us that based on what Moses saw – and what was subsequently handed down from generation to generation – Rabban Gamliel fashioned a picture of the moon in its various phases and would ask witnesses who claimed to see the new moon, “Did you see such or did you see such?” as a means of ascertaining whether they had indeed see the new moon. Thus, we see that the mitzvah of sanctifying the new month contains such exact specifications that Moses only fully understood it after G-d showed him the new moon.
(To be continued)