How do we know salvation is entirely by God's grace?

Scriptures such as Ephesians 2:8-9 proclaim that '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 emphasizes that salvation cannot be earned or achieved through human actions or decisions but is a pure gift from God. Additionally, it reflects the fundamental tenets of Reformed theology which asserts that God is the author of salvation, calling His elect to faith and regeneration through the Holy Spirit, affirming that our coming to faith is entirely due to His gracious initiative. Thus, the doctrine of salvation by grace alone underscores the mercy and power of God rather than any effort on our part.