Matthew 12:7

But if ye had known what this meaneth, I desire mercy and not sacrifice, ye would not have condemned the guiltless.

Christ said the disciples were guiltless. Therefore, he was not attempting to justify their conduct on the basis that David had also been guilty of sabbath breaking. Christ's quotation from Hosea 6:6 (See more on this under Matthew 9:13) was a plain reference to the corruption and guilt of the Pharisees, and suggests that a proper attitude of mercy in their hearts would have rejected the criticism of this action before it was made. The real trouble was not in Christ and his disciples but in the hearts of the Pharisees.