What a virtuous action that was, when David wished rather to spare the king his enemy, though he could have injured him! How useful, too, it was, for it helped him when he succeeded to the throne. For all learned to be faithful to their king and not to seize the kingdom but to fear and reverence him. Thus what is virtuous was preferred to what was useful, and then usefulness followed on what was virtuous.
It was not without God’s influence, you see, that he [David] succeeded in prevailing over those frenzied men [his soldiers who wished to kill Saul]: the grace of God was found on the inspired man’s lips, adding a sort of inducement to those words. It was, however, no slight contribution that David also made: since he had formed them in the past, consequently in the critical moment he found them ready and willing. It was not as leader of troops, you see, but as priest he commanded them, and that cave was a church on that occasion: like someone appointed as bishop, he delivered a homily to them, and after this homily he offered a kind of remarkable and unusual sacrifice, not sacrificing a calf, not slaying a lamb, but—what was of greater value than these—he offered to God gentleness and clemency, sacrificing irrational resentment, slaying anger and mortifying the limbs that are on the earth. He acted as victim, priest and altar: everything came from him—the thought that offered gentleness and clemency, the clemency and gentleness and the heart in which they were offered.
As a Christian judge, you must play the part of a loving father, you must show anger for wrongdoing but remember to make allowance for human weakness; do not indulge your inclination to seek vengeance for the vile acts of sinners, but direct your effort to the cure of the sinners’ wounds.… There is also that well-known example of forbearance on the part of holy David, when his enemy was delivered into his hands and he spared him, an example which shines with greater luster from the fact that he had power to act otherwise. Do not, then, let your power of punishment make you harsh, when the necessity of inquiry did not shake your spirit of mildness.
And David restrained his men with his words, etc. And the Lord restrained the severity of his disciples, who wished the impious to perish, by saying: Do not judge, and you will not be judged (Matthew VII). Do not condemn, and you will not be condemned (Luke VI). And elsewhere: For God did not send his Son into the world to judge the world, but that the world might be saved through him (John III), and so on of this kind, and he did not permit them to take immediate vengeance on the wrongdoers, but rather to love the correction of those who amend their ways.
Moreover, Saul rising from the cave, etc. The keepers of the Lord's tomb, who, having fallen prostrate through fear of the approaching angel and had become like dead men, and fleeing from the tomb, nonetheless continued the evil schemes against the Lord, saying that his disciples had come at night and stolen him away while they were sleeping. Which can also be rightly understood of those who placed guards at the tomb (Matthew XXVIII); who, even though they withdrew from guarding the tomb of the Lord with groans and confusion, nonetheless did not turn away from their intent of persecuting his faith with raging steps. With these both having been driven away from the watch of the tomb, the Lord himself did not delay to gradually reveal the glory of his resurrection, which he had assumed secretly, to his followers. And with this truth confirmed and taught, soon through them thundered the proclamation of free preaching, calling back benignly to the remedy of repentance and his love those who had turned away from him, his persecutors. To those whom he reconciled to himself with the first words of humanity and piety, he diligently taught some of them to look back after him, that is, to repent of their crime against God.
[AD 397] Ambrose of Milan on 1 Samuel 24:6-7