Irenaeus of Lyons, Against Heresies 4.17

The prophets make it perfectly clear that God commanded certain observances in the law not because He needs our service, but for our own sake. The Lord has taught the same truth just as plainly: He does not need our offerings, but accepts them for the sake of the one who offers them. When He saw His people neglecting justice and turning away from the love of God, yet imagining they could appease Him through sacrifices and other ceremonial observances, Samuel told them: "God does not want burnt offerings and sacrifices, but wants you to listen to His voice. Obedience is better than sacrifice, and to listen is better than the fat of rams" (1 Sam 15:22). David says the same: "You did not want sacrifice and offering, but You have given me an open ear. You did not ask for burnt offerings and sin offerings" (Ps 40:6). He was teaching them that God desires obedience, which saves them, rather than sacrifices and burnt offerings, which do nothing to make them just—and in saying this he was also prophesying the New Testament. The fiftieth Psalm states this even more clearly: "If You had wanted sacrifice, I would have given it; You take no delight in burnt offerings. The sacrifice acceptable to God is a broken spirit; a broken and contrite heart, O God, You will not despise" (Ps 51:16-17). Since God needs nothing, the preceding Psalm declares: "I will not accept a bull from your house, or goats from your folds. For every beast of the forest is Mine, the cattle on a thousand hills. I know all the birds of the air, and all that moves in the field is Mine. If I were hungry, I would not tell you, for the world and its fullness are Mine. Do I eat the flesh of bulls, or drink the blood of goats?" (Ps 50:9-13). Then, so that no one would think He rejects these things out of anger, He gives them counsel: "Offer to God a sacrifice of thanksgiving, and pay your vows to the Most High. Call upon Me in the day of trouble; I will deliver you, and you shall glorify Me" (Ps 50:14-15). He rejects the very things by which sinners thought they could appease Him, showing that He needs nothing; but He urges and admonishes them toward the things by which a person is justified and draws near to God. Isaiah says the same: "What to Me is the multitude of your sacrifices? says the Lord; I have had enough of burnt offerings of rams and the fat of well-fed beasts" (Is 1:11). After rejecting burnt offerings, sacrifices, grain offerings, new moons, Sabbaths, festivals, and the whole train of observances that follow them, He points them to what truly saves: "Wash yourselves; make yourselves clean; remove the evil of your deeds from before My eyes; cease to do evil, learn to do good; seek justice, correct oppression; bring justice to the fatherless, plead the widow's cause. Come now, let us reason together, says the Lord" (Is 1:16-18). He does not turn away their sacrifices like a man moved by emotion, as many dare to claim, but in mercy toward their misguided zeal He points them to the true sacrifice—one which, when offered, propitiates God so that they may receive life from Him.