Moses offers a full answer to this vital question in his account of the life of Abraham, who is justly called the father of our faith. In Genesis 15:6 we are told that Abraham “believed the Lord, and he counted it to him as righteousness.” The apostle James cites this verse and claims that because of his faith Abraham became the “friend of God” (James 2:23). The apostle Paul likewise appeals to this verse to establish the fact that Abraham’s pattern of justifying faith is normative for all that are righteous before God (Rom. 4:22–25), that it is not by works of the Law, rather by “hearing with faith” that we are justified (Gal. 3:5–6).

Ligonier.org