For by grace you have been saved through faith. (Ephesians 2:8)
The New Testament correlates faith and grace to make sure that we do not boast in what grace alone achieves.
One of the most familiar examples goes like this: “For by grace you have been saved through faith” (Ephesians 2:8). By grace, through faith. There’s the correlation that guards the freedom of grace.
Faith is the act of our soul that turns away from our own insufficiency to the free and all-sufficient resources of God. Faith focuses on the freedom of God to dispense grace to the unworthy. It banks on the bounty of God.
Therefore faith, by its very nature, nullifies boasting and fits with grace. Wherever faith looks, it sees grace behind every praiseworthy act. So it cannot boast, except in the Lord.
So Paul, after saying that salvation is by grace through faith, says, “And this is not of your own doing; it is the gift of God, not a result of works, so that no one may boast” (Ephesians 2:8–9). Faith cannot boast in human goodness or competence or wisdom, because faith focuses on the free, all-supplying grace of God. Whatever goodness faith sees, it sees as the fruit of grace.
When it looks at our “wisdom from God, righteousness and sanctification and redemption,” it says, “Let the one who boasts, boast in the Lord” (1 Corinthians 1:30–31).