How do we know that salvation is only by grace?

In Reformed theology, salvation is understood as a work of God's sovereign grace, which means it is rooted entirely in God's action rather than human merit. Ephesians 2:8-9 clearly states that we are saved by grace through faith, and not of ourselves, lest anyone should boast. This grace is realized through the redemptive work of Christ, who paid the full price for sin. Romans 3:23 reinforces the idea that all have sinned, emphasizing our inability to achieve righteousness on our own. Thus, it is only through Christ's righteousness imputed to believers that anyone can stand before God.