Mishnah Yoma on Reviewing One's Torah Learning Often

It is a great virtue to review one's Torah learning regularly and consistently. It is reported that the Vilna Gaon reviewed the entire Babylonian Talmud every month (which normally takes 7.5 years by the Daf Yomi cycle), and that he reviewed the entirety of the tractates "Shabbat" and "Eruvin" every Sabbath. The word "Mishnah" means repetition, and it is especially important to verbally recite mishnayot often, so that they are always fresh in one's mind.

This virtue is brought to light in the Mishnah itself, in tractate "Yoma". This mishnah describes the preparations made by the Kohen Gadol during the week before the Yom Kippur avodah:

"They assigned the Kohen Gadol two elders from among the elders of the Sanhedrin. They would read to him from the Torah passage that describes the order of the Temple service on the Day of Atonement, and elaborate on its laws. And they would say to him: 'My master, Kohen Gadol, you should read this passage with your own mouth, in case you have forgotten, or in case you have not learned.'" -- Mishnah, Yoma 1:3.

Notice that the suggestion that the Kohen Gadol read the passages out loud, in case he forgot or didn't really learn them, is not taken an insult to the Kohen Gadol's stature. We learn from this that even the greatest Torah scholars should review their learning often and with great care.

Midrash Rabbah Eichah on Scholars of Torah

"Rabbi Yehudah haNasi [the redactor of the Mishnah] would send Rabbi Assi and Rabbi Ami to go forth and rectify the cities of the Land of Israel. They would enter the cities, and they would say to the townsfolk, 'Bring the protectors of the city to us.' The townsfolk would bring the head of the town guard and the watchman to them. They would say to the townsfolk, 'These are the protectors of the city? These are the destroyers of the city!' The townsfolk would then say to Rabbi Assi and Rabbi Ami, 'And who then are the protectors of the city?' The two scholars would say to the townsfolk, 'The guards of the city are the teachers of Scripture and the teachers of Mishnah, for they are studying and learning and upholding the Torah, by day and by night, in accordance with that which Scripture states, 'This book of the Torah shall not depart from your mouth; rather, you should study it day and night' (Joshua 1:8). And so the verse states, 'If YHVH will not build the house, in vain do its builders labor on it; if YHVH will not guard the city, in vain is the watchman vigilant' (Psalms 127:1)."

-- Midrash Rabbah, Eichah 1.2