How do we know that grace alone is sufficient for our salvation?

The doctrine of grace alone asserts that salvation is entirely the work of God, with no assistance required from human actions. This is supported by biblical passages like Ephesians 2:8-9, which says that by grace we are saved through faith, emphasizing that it is not by works. The passage in Matthew 12 reflects the struggle between self-righteousness and the grace offered through Christ, showing that turning to personal efforts can lead to further condemnation. True salvation comes only from faith in Christ, who fulfilled all righteousness for our behalf.