Abraham heard from God and believed. Abraham’s faith caused him to leave everything behind and live the rest of his life as a stranger in a strange land. Abraham’s faith trusted that he and Sarah would have a child, even though that seemed impossible. Abraham’s faith was even willing to sacrifice the promised son, believing that God would raise him from the dead (Hebrews 11:9). Because of Abraham’s example of faith, the Bible points to him as the grandfather of faith, as it were. All who similarly trust in the Lord are “sons of Abraham.”
“For ye are all the children of God by faith in Christ Jesus. For as many of you as have been baptized into Christ have put on Christ. There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus. And if ye be Christ's, then are ye Abraham's seed, and heirs according to the promise.” Galatians 3:26–29
God had promised Abraham that “all peoples on earth will be blessed through you” (Genesis 12:3). One way this prophecy is fulfilled is through the salvation that God grants to us, by grace through faith.
“Know ye therefore that they which are of faith, the same are the children of Abraham. And the scripture, foreseeing that God would justify the heathen through faith, preached before the gospel unto Abraham, saying, In thee shall all nations be blessed. So then they which be of faith are blessed with faithful Abraham.” Galatians 3:7–9