Saul armed David with his armour— i.e. Not with his own armour, for Saul was of too great a size; but he ordered a helmet and coat of mail to be brought out of his armoury for him.
Related Commentaries of 1 Samuel 17:38
1 Samuel 17:38
38 And Saul armed Davidj with his armour, and he put an helmet of brass upon his head; also he armed him with a coat of mail.