Albert Barnes Commentary Isaiah 48:21

"And they thirsted not when he led them through the deserts; he caused the waters to flow out of the rock for them; he clave the rock also, and the waters gushed out." — Isaiah 48:21 (ASV)

And they thirsted not - This is part of the reason they would be called to celebrate his name. It was not merely that he had redeemed them, but that he had abundantly provided for their needs in the desert and guided them safely through the pathless wilderness to their own land (see the notes at Isaiah 35:6-7; Isaiah 41:17–18).

He caused the waters to flow out of the rock for them - The allusion here is undoubtedly to the fact that God caused the waters to flow out of the rock that Moses struck in the wilderness (Exodus 17:6; Numbers 20:11).

This is not to be regarded as literally true that God would, in a similar manner, strike the rocks and cause waters to flow by miracle on their return from Babylon. There is no record that any such event took place, and it is not necessary to understand this passage in that way.

It is a part of the triumphant song which they are represented as singing after their return to their own land. In that song, they celebrate his gracious interposition in language that was familiar to them, and by illustrations that were well known.

They therefore speak of his mercy to them as if he had struck the rock in the desert on their return and caused the waters to flow. The sense is that his mercy to them then was similar to his goodness to their fathers when he led them to the land of promise. He met all their necessities, and his gracious interposition was experienced all the way as really as though he had struck the rock or caused cool and refreshing fountains to break out in the desert.