Or HaChaim on Deuteronomy 33:9/אור החיים על דברים ל״ג:ט׳

1 האומר…יורו משפטיך ליעקב. "Who says ….they shall teach Your laws to Jacob." We may explain this verse best according to Baba Batra 60 where the Talmud relates that Rabbi Yannai had a tree the branches of which overhung the adjoining street causing inconvenience to the passers-by. He was called upon to expound the law in a similar situation and asked to be given until the morrow before presiding over this litigation. During the intervening night he gave instructions to cut down the branches of his tree which overhung the street so as not to be accused of being himself guilty of an offence which he was supposed to adjudicate. [The Talmud explains that originally Rabbi Yannai had thought that the shade provided by his tree for the passers-by outweighed any damage it could cause to the passers-by who failed to look where they were going. Ed.] The word האומר is an allusion to the kind of judge qualified to sit in judgment of others, i.e. only people who ensure that their own house is in order may judge others. In order to face one's parents and criticise them one must first be free from guilt himself.

2Another message contained in this verse refers to the Torah's injunction in Deut. 16,18 that the judges should be from the respective tribes. Moses adds here that inasmuch as the tribe of Levi had demonstrated during the episode of the golden calf that they did not show favouritism even to their closest family members if the latter were guilty, that they could preside in judgment even over litigations involving members of other tribes. This is the meaning of יורו משפטיך ליעקב, i.e. they can judge any descendant of Jacob.