C. F. Keil and Franz Delitzsch on 1 Samuel 21:4

1Sa 21:4

The priest answered that he had no common bread, but only holy bread, viz., according to 1Sa 21:6, shew-bread that had been removed, which none but priests were allowed to eat, and that in a sacred place; but that he was willing to give him some of these loaves, as David had said that he was travelling upon an important mission from the king, provided only that “the young men had kept themselves at least from women,” i.e., had not been defiled by sexual intercourse (Lev 15:18). If they were clean at any rate in this respect, he would in such a case of necessity depart from the Levitical law concerning the eating of the shew-bread, for the sake of observing the higher commandment of love to a neighbour (Lev 19:18; cf. Mat 12:5-6; Mar 2:25-26).When Mark (Mar 2:26) assigns this action to the days of Abiathar the high priest, the statement rests upon an error of memory, in which Ahimelech is confounded with Abiathar.