He clave the rocks in the wilderness - There were two occasions on which the rock was smitten for water; one Exodus 17:6 at Mount Horeb, shortly after they came out of Egypt; and the other Numbers 20:11, when they had nearly ceased their wanderings in the wilderness. Hence, the plural term (rocks) is used here.
And gave them drink as out of the great depths - As if he had formed a lake or an ocean, furnishing an inexhaustible supply.