Adam Clarke on Deuteronomy 33:10

They shall teach Jacob, etc. - This was the office of the Levites, to teach, by their significant service and typical ceremonies, the way of righteousness and truth to the children of Israel. And of their faithfulness in this respect God bears testimony by the prophet, "My covenant was with him of life and peace," Mal 2:5; and, "The law of truth was in his mouth, and iniquity was not found in his lips: he walked with me in peace and equity, and did turn many away from iniquity;" Mal 2:6. These words are a sufficient comment on the words of the text.