How do we know that only God can save sinners?

Salvation is entirely of the Lord; it begins with the recognition that every sinner has a debt before God that they cannot repay due to their sinful nature. From the fall of Adam, all humanity is born with a transgression of God’s law which incurs a debt of death. The only acceptable payment for this debt is through the sacrificial death of Jesus Christ, who alone is capable of bearing the sin of His people. As articulated throughout Scripture, particularly in passages like Ephesians 1:4-5, salvation is a work of God's grace, not based on human efforts or merit. Therefore, unless God intervenes and grants a sinner faith, they remain bound to their state of spiritual death.