Tosefta su Salmi 119:126

Originally, when the Torah would get forgotten from the Jewish people the elders would swallow it (i.e. the Torah) between themselves, [and not publicly teach it to the masses in great detail] as it is said, “And behold, Boaz was coming from Bet Lechem and he said to the harvesters, ‘Hashem is with you’. And they said to him, ‘May Hashem bless you.’” (Ruth 2:4) And [also] it says, “Hashem is with you, mighty warrior.” (Judges 6:12) And [also] it says, “… and do not scorn your mother when she has grown old.” (Proverbs 23:22)5 “It is time to do for Hashem, they have forsaken Your Torah.” (Psalms 119:126)

Hillel the Elder says, “At the time when they gather in you should spread, and at the time when they spread you should gather in.” At the time that you see that the Torah is beloved to all of the Jewish people and everyone rejoices in it, you should spread it (i.e. teach it) as it is said, “The one that spreads gathers in more ...” (Proverbs 11:24) And at the time that you see that the Torah is being forgotten from the Jewish people and no one is paying attention to it, gather it in (i.e. learn it privately to yourself and do not teach), as it is said, “It is time to do for Hashem, they have forsaken your Torah.” (Psalsms 119:126) Rebbi Meir says, “[If] they have forsaken your Torah, [then] it is time to do for Hashem [and teach the Torah to the masses even with more force than before].”