(Devarim, Ibid. 13) "Which I command you this day.": Whence is it derived that if one heard a word (of Torah) from a minor it is as if he heard it from a sage? From (Koheleth 12:11) "The words of the wise are like goads, etc." What is more, if one hears (words of Torah) from a sage, it is as if he hears them from Sanhedrin, it being written (Ibid.) "the man of the gatherings," "gatherings" alluding to Sanhedrin, viz. (Bamidbar 11:16) "Gather unto Me seventy men from the elders of Israel."
And if one hears from Sanhedrin, it is as if he hears from Moses, viz. (Koheleth, Ibid.) "given by one shepherd (Moses)." And (Isaiah 63:11) "And they remembered the days of old, Moses and his people. Where is he who brought them up from the Sea? the shepherd of His flock? who placed in their midst His holy spirit?" And, what is more, if one hears from Moses, it is as if he hears from the Holy One Blessed be He, viz.: "given by one Shepherd," and (Psalms 80:2) "Shepherd of Israel hear, Leader of Joshua as a flock — Dweller above the cherubs, appear!" And it is written (Devarim 6:4) "Hear, O Israel, the L-rd our G-d, the L-rd is One."