How do we know salvation is entirely by grace?

Salvation's nature as a work of grace is articulated throughout Scripture, especially in Ephesians 2:8-9, which proclaims that it is by grace we are saved through faith, and this not of ourselves; it is the gift of God, not of works, lest any man should boast. The doctrine of total depravity teaches that because of sin, man is wholly incapable of saving himself. As noted in Romans 3:10, there is none righteous, no, not one. Hence, God's intervention through grace becomes essential. The believer’s plea for salvation is directed towards God, as it is ultimately He who chooses to save (Romans 10:13).