It is beneath the dignity of a prophet to hold people captive, after the war is over [and after their ransom is being paid.] For you the possessions of this world is important (and that is why you want to keep the captives, humiliate them and even kill them) while it is Hereafter that God recommends to you and, of course [He knows what is the best for you as], God is the Most Knowledgeable, the Most High.