How do we know grace is the basis for salvation?

Ephesians 2:8-9 states, 'For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: Not of works, lest any man should boast.' This passage clearly delineates that human efforts cannot earn salvation; it is solely a gift from God. Grace signifies God's unmerited favor towards those who are undeserving, and throughout Scripture, we see examples of this grace in action, such as in the stories of Abraham, Sarah, and Noah, whose salvation was not based on their merits but entirely on God's grace and promises.