Psalms 78:15

15.He clave the rocks in the wilderness. The Psalmist produces another evidence of the fatherly love by which God testified the greatness of the care which he exercised about the welfare of this people. It is not simply said that God gave them drink, but that he did this in a miraculous manner. Streams, it is true, sometimes issue from rocks, but the rock which Moses smote was completely dry. Whence it is evident, that the water was not brought forth from any spring, but that it was made to flow from the profoundest deeps, as if it had been said, from the very center of the earth. Those, therefore, who have interpreted this passage as meaning, that the Israelites drank in the bottomless deeps, because the waters flowed in great abundance, have failed in giving the true explanation. Moses, in his history of the miracle, rather enhances its greatness, by intimating, that God commanded those waters to come gushing from the remotest veins.

The same truth is confirmed in the following verse, in which it is stated, that where there had not been a single drop of water before there was a large and mighty river. Had there only sprung out of the rock a small rivulet, ungodly men might have had some apparent ground for cavilling at, and underrating the goodness of God, but when the water gushed out in such copious abundance all on a sudden, who does not see that the ordinary course of nature was changed, rather than that some vein or spring which lay hidden in the earth was opened?