Parashas Bo · Shemos 12:2 · TT note 7
Chabad.org — English translation + Rashi
Torah Temimah on Shemos 12:2, note 7 (on לָכֶם) points to Rosh Hashanah 25b.
Sefaria — Exodus 12:2
Sefaria — Torah Temimah on Exodus 12:2
Sefaria — Rosh Hashanah 25b
E-Daf — Rosh Hashanah 25b
English: There is no greater expert for the public in Israel than Moshe our teacher, and yet the Holy One, blessed be He, said to him: only when Aharon is with you — as it is written, “Hashem said to Moshe and to Aharon in the land of Egypt, saying: This month shall be for you.”
Derash on לָכֶם (plural): even a single outstanding expert may not sanctify the month alone; a court is required.
Sanctification of the new month is not left to an individual, however expert; the verse’s plural address models the need for a court.