Adam Clarke on Deuteronomy 33:11

Bless, Lord, his substance - The blessing of God to the tribe of Levi was peculiarly necessary, because they had no inheritance among the children of Israel, and lived more immediately than others upon the providence of God. Yet, as they lived by the offerings of the people and the tithes, the increase of their substance necessarily implied the increase of the people at large: the more fruitful the land was, the more abundant would the tithes of the Levites be; and thus in the increased fertility of the land the substance of Levi would be blessed.