Or HaChaim on Deuteronomy 33:8/אור החיים על דברים ל״ג:ח׳

1 וללוי אמר תמיך ואוריך לאיש חסידך, "And concerning Levi he said: "Let your Tummim and your Urim be with Your faithful one." This is a prayer that Levi should continue forever to be qualified to perform the respective duties of the Levites and the priests.

2אשר נסיתו במסה, "whom You have tested at Massah." Seeing that Jacob (Genesis 49,5) had expressed himself negatively concerning any union of Shimon and Levi, cursing their anger, Moses goes on record to say that in the meantime the Levites had proved at Massah that they (by themselves) did not display anger and transgress G'd's commands. Instead of having tested G'd's patience there (Exodus 17,7) where the people questioned G'd's ability to provide them with water) as had the other tribes, this tribe had stood the test of loyalty (and had not participated in that complaint). [There may be an allusion to this in that paragraph as at the beginning the Torah speaks about the whole community arriving at that place whereas when speaking about who complained the word "whole" is absent. Ed.]