Faith—and only faith—is the instrumental means of justification. In other words, it is through faith alone that we lay hold of or appropriate the sole basis for our justification, namely, Christ’s righteousness (Rom. 4). Faith itself is not the righteousness upon which God declares us righteous in His sight; only the obedience of Christ is the evidence, as it were, upon which our Creator pronounces His verdict that we are just and heirs of eternal life (5:12–21). Yet, the righteousness of Christ cannot be ours apart from our receiving and resting in Christ alone—it will not be imputed to us apart from faith.
But why is faith and not something else the instrumental means of justification? To answer this question, we must understand something of the character of saving faith. First, in keeping with the truth that our salvation is due to God’s mercy alone, faith is the only instrumental means of justification because faith is the gift of God. When Paul speaks of the “gift of God” in Ephesians 2:8, he is not referring merely to the grace of God described earlier in the same verse. It would be redundant to refer to grace as a gift because by definition grace is a gift, and furthermore, the grammar of the verse demands that “gift of God” refer to the entire grouping of grace, salvation, and faith in verse 8. The perfect righteousness of Christ is God’s gift to us, and even the means by which we receive it is the Lord’s gift given to us in regeneration. Our election unto salvation that bears fruit in justifying faith “depends not on human will or exertion, but on God, who has mercy” (Rom. 9:16), and no one whom our Creator mercifully draws to Himself fails to trust in Christ (John 6:37–40). Even though we exercise faith, we have it because God gives it to us through the work of His Son, Jesus Christ, who is the author and finisher of our faith (Heb. 12:2).
Of course, today’s passage says that the good works we do after we are justified are also gifts of God (Eph. 2:10), but they are not the means by which we lay hold of Christ’s righteousness. Why? Because although faith is something we do—we trust in Christ—the character of saving or justifying faith is to rest and receive, not to offer something meritorious to God. Abraham’s faith is the paradigm of justifying faith—he received the promise of God and trusted in it, not offering anything else to conceive the promised son Isaac, for he had nothing to give (Gen. 15:1–6; Rom. 4:16–25). Saving faith can be likened to an open hand that simply receives what is offered, admitting that we have nothing in ourselves.