Sforno on Deuteronomy 33:8/ספורנו על דברים ל״ג:ח׳

1תומיך ואוריך לאיש חסידך, Moses refers to G’d having given to Aaron who was the outstanding member of the tribe of Levi, the pious tribe, the urim and tumim lodged within his breastplate pouch. The Talmud Yuma 73, derives from the above that any priest who speaks with holy spirit is of the calibre that when he employs the urim and tumim to address enquiries to G’d, he will receive G’d’s answer to such enquiries. Hence the word “איש,” a man of lofty spiritual standing, as if to underscore that character trait.

2אשר נסיתו במסה, Moses reminds G’d that in all the various tests (Numbers 14,22) that the Jewish people had subjected Him to, the tribe of Levi had never been a participant in such demonstrations of lack of faith. This was also why the decree which G’d imposed on the generation of the spies did not apply to them, and the Levites that were of age at that time did not die in the desert.

3תריבהו על מי מריבה, You have challenged them at the waters of strife, as a result of which You deprived the people of the two outstanding heads of the tribe of Levi.