John Gill

And he said unto them,.... By way of answer to their question, and which was a full one, and enough to silence them: have ye never read what David did; referring to the history in Sa1 21:1. when he had need: of bread, was in great necessity, and in the utmost distress: and was an hungered, he, and they that were with him? which was a justifiable reason for what he and his company did; as it was for the action of the disciples; being in a like case, and therefore very appropriate to the purpose; See Gill on Mat 12:3.