How do we know that salvation is by God's mercy and not our works?

In Romans 9, the Apostle Paul explains that salvation is not of him that wills or runs but of God who shows mercy (Romans 9:16). This establishes the truth that our salvation is not contingent upon our works or choices but rather upon God's sovereign will and election. Furthermore, God's choice of individuals, as exemplified by Jacob and Esau, demonstrates His authority to extend mercy as He sees fit, aligning perfectly with the theological assertion that salvation is a gift from God, rooted in His grace, and devoid of human merit.