ייִדישער מחשבֿה אויף מלאכי 2:6

Likewise, my brother, if one rectifies only himself, he will have a small merit. But if one rectifies himself and many other people, he will have his merit multiplied according to the merits of all the people who he rectified to G-d, as our sages said: "Whoever brings merit to the masses will not come to any sin" (Avot 5:18), and they said: "Moshe was righteous and caused the multitude to become righteous, the merit of the multitudes is attributed to him, as written 'he performed the righteousness of G-d and His judgments with Israel", and the wise man said: "But to them that rebuke shall be delight, and a good blessing shall come upon them" (Mishlei 24:25), and "The law of truth was in his mouth - and turned many away from iniquity" (Malachi 2:6), and "those who bring merit to the multitudes will be like the stars forever and ever" (Daniel 12:3).