The Jews, by virtue of their being the physical descendants of Abraham are his children in the natural sense. However, the Scriptures speak of a sense in which Abraham’s natural descendents are not necessarily his children, unless they act as he acted. Paul makes this argument in Galatians, chapter three, by concluding that all people, whether Jew or gentile, are children of Abraham only if they believe God. In other words, since Abraham’s faith was credited to him as righteousness, only the righteous or those who believe God are Abraham’s children in the spiritual sense.
God made a covenant with Abraham in Genesis 12:3 that all the nations of the world would be blessed in him, if he would leave the land of his fathers and go to a land that God would show him. This covenant was not dependent upon anything but Abraham’s believing God (Genesis 15:6), for it was made before Abraham had any children, and before the covenant of circumcision. It was made while Abraham was still a heathen and an idolater in the land of Ur and before the Law was given to man. Paul’s argument is that it would be unethical, even according to a man’s covenant, to add stipulations to a contract after the covenant was agreed upon by both parties (Galatians 3:15). Therefore, those who came to Galatia, arguing that gentiles had to become circumcised (Galatians 5:6-7) in order to be saved, were wrong. Their argument is not according to the Scriptures and, therefore, cannot represent God’s demands.
Contrariwise, those who make their boast in the Law for salvation are under its curse, if they do not continue in all the words of the Law (Galatians 3:10). While it is true, if a person is perfect in obedience to the Law, that one shall live, it is also true that the Scriptures show there is none righteous (Psalm 14:1-3). The fact is that we are born in unrighteousness, because the Scriptures claim that no one is able to bring a clean thing from that which is unclean (Job 14:4; Psalm 51:5, cp. Haggai 2:11-15). Therefore, anyone who boasts in the Law is under the curse of the Law which requires his death. The Law cannot of itself give life. Even those who are under the Law must trust God for their salvation (Habakkuk 2:4). No one can depend upon his own obedience to the Law, which obedience is at best imperfect. All, whether Jew or gentile, must depend upon the grace of God, and that requires trust—faith in God.
Therefore, if Abraham was declared righteous, because he believed God, then anyone who believes God is also righteous. That is, God does not hold a man’s sins against him, no matter how unrighteous he had been, if that one trusts God for his deliverance and salvation. While Abraham was yet an idolater, he believed God, and he was accounted righteous! How so? It is done through the cross of Christ. He has redeemed all by taking the responsibility of all our sins upon himself. Jesus made himself responsible for our transgressions and paid the penalty for us (Galatians 3:13). The Law claims our life, but Jesus paid the penalty that the Law required. We are now free from any claim the Law has upon us. This is the grace of God, and it is obtained through faith. We trust God—that is, we believe him when he says he loves us and has taken responsibility for all our transgressions. We cannot obtain his favor through our works of righteousness. We obtain his favor by simply believing he will do what he claims he will do, or in the matter of our salvation, that he has done what he claims he has done for us. To doubt this is like not trusting one’s Friend.