The philosophers postulate four kinds of causes to be observed in the outworking of things. If we look at these, however, we will find that, as far as the establishment of our salvation is concerned, none of them has anything to do with works. For Scripture everywhere proclaims that the EFFICIENT CAUSE of our obtaining eternal life is the mercy of the Heavenly Father and his freely given love toward us. Surely the MATERIAL CAUSE is Christ, with his obedience, through which he acquired righteousness for us. What shall we say is the FORMAL OR INSTRUMENTAL cause but faith? And John includes these three in one sentence when he says: “God so loved the world that he gave his only-begotten Son that everyone who believes in him may not perish but have eternal life” [John 3:16]. As for the FINAL CAUSE, the apostle testifies that it consists both in the proof of divine justice and in the praise of God’s goodness, and in the same place he expressly mentions three others. For so he speaks to the Romans: “All have sinned and lack the glory of God; moreover, they are justified freely by his grace” [Rom. 3:23–24; cf. Eph. 1:6, cf. Vg.].
Here you have THE HEAD AND PRIMAL SOURCE: that God embraced us with his free mercy. There follows: “Through the redemption which is in Christ Jesus” [Rom. 3:24]. Here you have, as it were, the MATERIAL CAUSE by which righteousness is brought about for us. In the words “through faith in his blood” [Rom. 3:25 p.], is shown the INSTRUMENTAL CAUSE whereby the righteousness of Christ is applied to us. Lastly, he adds the FINAL CAUSE when, to demonstrate his righteousness, he says, “In order that he himself may be righteous, and the justifier of him who has faith in Christ” [Rom. 3:26, Vg.]. And to note also, by the way, that this righteousness stands upon reconciliation, he expressly states that Christ was given as reconciliation.
Thus also in the first chapter of Ephesians he teaches that we are received into grace by God out of sheer mercy, that this comes about by Christ’s intercession and is apprehended by faith, and that all things exist to the end that the glory of divine goodness may fully shine forth [Eph. 1:3–14].
Since we see that every particle of our salvation stands thus outside of us, why is it that we still trust or glory in works? The most avowed enemies of divine grace cannot stir up any controversy with us concerning either the efficient or the final cause, unless they would deny the whole of Scripture. They falsely represent the material and the formal cause, as if our works held half the place along with faith and Christ’s righteousness. But Scripture cries out against this also, simply affirming that Christ is for us both righteousness and life, and that this benefit of righteousness is possessed by faith alone.
John Calvin, Institutes of the Christian Religion, 3.14.17