Probably because of its first verse, Psalm 143 received the title, “A Psalm of David against Goliath.” Augustine began his comments by referring to the fight and the victory of Christ, “our David,” over the giant. He went on to speak of the “inner warrior” who has to engage in the inner combat between flesh and spirit. And don’t miss what the greatest victory may be.
“Blessed is the Lord my God who teaches my hands to fight and my fingers to war”(Ps 143:1). If you want to fight without being taught, you’ll be defeated and damned. First, then, subject yourself to God, and then he will teach and help you fight, and you may say, “He teaches my hands to fight and my fingers to war.”
While you’re fighting, you’re in danger, of course, so while the fight continues, say what follows in the Psalm: “My mercy, don’t let me be defeated!” What does “my mercy” mean? “You show me mercy, you’re merciful to me?” Or: “You have given it to me so I will be merciful, too?” Victory over our enemy is never greater than when we are merciful. The enemy is preparing false charges to bring you to court, but he can’t make false accusations because there’s no one he could make them to. If we were to be judged by a human judge, he could lie and deceive and burden us with false complaints; but because our case is before a judge who cannot be deceived, the enemy goes around and tries to seduce us so that he’ll have real reasons for his accusations. When human frailty succumbs to his deceits, let it with humility acknowledge it and engage in works of mercy and devotion. All things are wiped away when with honest hearts and full confidence we say to him who watches, “Forgive us, just as we forgive others” (Mt 6:12). Say it with all your heart, say it with full confidence, say it without concern: “Forgive us, just as we forgive others” and don’t forgive us if we don’t forgive others. Even if we don’t say, “Don’t forgive us if we don’t forgive others,” in fact he does not forgive if we do not forgive. ... “You want me to forgive you,” he says, “well then, you forgive others.”
There’s another work of mercy. You want me to give you something? Then you give something.” There’s a place in the Gospel where it says, “Forgive and you will be forgiven; give and it will be given to you” (Lk 6:37, 38). “I have something against you,” he says, “and you have something against someone else. Forgive him and I’ll forgive you. You ask for something from me, and someone else asks something from you. Give and I will give.” And what is it that forgives, that gives? Is it not love? And where does love come from if not “through the Holy Spirit that has been given to us” (Rom 5:5)? If, then, our enemy is defeated by works of mercy, and if we couldn’t have works of mercy unless we had love, and we would have no love unless we received it through the Holy Spirit, then he is teaching our hands for battle and our fingers for war; and we rightly say, “My mercy,” to him from whom we have the ability to be merciful ourselves. “There will be judgment without mercy for anyone who does not himself show mercy” (Jas 2:13)....
What then? What follows? “Mercy exalts itself above judgment.” Brothers and sisters, what does this mean? Mercy is placed above judgment. If a work of mercy is found in someone, even though he may have something to be punished, the fire of sin is extinguished as if by a wave of mercy. “Mercy exalts itself about judgment.” What, then, when God helps such people and frees them and forgives them, is he being unjust? Of course not! Even then he is just: mercy does not take away justice nor justice mercy. See if he is not just: “Forgive, and I forgive; give and I give.” See if he is not just: “With what measure you measure it will be forgiven you” (Mt 7:2). Not that the measure is of the same kind, but there is the same measure in this respect: “Forgive, and I forgive. You have a measure of forgiveness to give; you’ll find that I have a measure of pardon for you to receive. You have a measure of pardon to give; you’ll find with me a measure of pardon to receive. (EnPs 143, 6-8; PL 37, 1860-62)