Jamieson, Fausset and Brown on Exodus 17:5

5. the Lord said unto Moses, &c.--not to smite the rebels, but the rock; not to bring a stream of blood from the breast of the offenders, but a stream of water from the granite cliffs. The cloud rested on a particular rock, just as the star rested on the house where the infant Saviour was lodged [Mt 2:9]. And from the rod-smitten rock there forthwith gushed a current of pure and refreshing water. It was perhaps the greatest miracle performed by Moses, and in many respects bore a resemblance to the greatest of Christ's: being done without ostentation and in the presence of a few chosen witnesses (1Co 10:4).