How do we know that salvation is by grace according to the Bible?

In Ephesians 2:8-9, the Apostle Paul explicitly affirms that salvation is a gift from God, emphasizing that it is by grace through faith. This means that human efforts or works cannot earn salvation; it is solely through God's unmerited favor. The sermon also mentions Apollos, who preached the message of grace, confirming that he understood the essence of salvation as initiated and sustained by God's grace. Historic Reformed theology consistently upholds this doctrine, emphasizing that salvation belongs wholly to the Lord and is rooted in His sovereign grace.