And of Levi he said, Let thy Thummim and thy Urim be with thy holy one, whom thou didst prove at Massah, and with whom thou didst strive at the waters of Meribah; Of Levi he said - Concerning the Urim and Thummim, see Exodus 28:30 (note).
Thy holy one - Aaron primarily, who was anointed the high priest of God, and whose office was the most holy that man could be invested with.
Therefore Aaron was called God's holy one, and the more especially so as he was the type of the Most Holy and blessed Jesus, from whom the Urim - all light and wisdom, and Thummim - all excellence, completion, and perfection, are derived.
Whom thou didst prove, etc. - God contended with Aaron as well as with Moses at the waters of Meribah, and excluded him from the promised land because he did not sanctify the Lord before the people.
From the words of St. Paul, 1 Corinthians 10:8-12, it is evident that these words, at least in a secondary sense, belong to Christ. He is the Holy One who was tempted by them at Massah, who suffered their manners in the wilderness, who slew 23,000 of the most incorrigible transgressors, and who brought them into the promised land by his deputy, Joshua, whose name and that of Jesus have the same signification.