First-century Jews took great pride in being descendants of Abraham, whom God chose to be His agent of blessing to the world and who was even called the “friend of God” (Gen. 12:1–3; James 2:23). But as we see in the New Testament, many of them believed that mere physical descent was sufficient to make them children of the patriarch (Luke 3:7–9). Scripture, however, tells us that the true children of Abraham and the inheritors of his blessing are those who do what Abraham did, namely, rest on the promises of God alone. To be a true child of Abraham is to share his spiritual condition, to trust in Jesus as Messiah. Physical descent from Abraham without faith in Christ doesn’t make one a child of Abraham, while sharing his faith without being descended from him makes one the patriarch’s true child (Gal. 3:1–14).
The Jews whom Jesus confronted after He declared Himself the light of the world apparently understood that Jesus was speaking of a spiritual sonship of Abraham when He rejected their claim to be Abraham’s children (John 8:39–40). We see evidence of this in today’s passage. The Jews claimed not to be illegitimate spiritual children but rather to be children of God (v. 41). On the surface, they had some scriptural justification for this, for Israel is called the son of God in the Old Testament (Hos. 11:1). But again, this reflects an idea that physical descent and Jewish blood is sufficient to make a person spiritually sound, to make him a child of God spiritually.
No one is more qualified to identify the true children of God than Jesus, who is the Son of God by nature. And as we see in John 8:42–47, Jesus rejected their claims of sonship. He rejected their claims because they rejected Him, for the mark of a true child of God is embracing Christ by faith. Those who do not do so reject the truth of God Himself. They show that their true Father is the devil, the liar who perverts truth and is a murderer (v. 44). Satan was the agent who tempted Adam and Eve, resulting in their spiritual death, and hence he is a spiritual murderer. And every descendant of Adam who rejects the truth of God revealed in Christ Jesus our Lord shows that they share the devil’s fallen nature (v. 47). To be outside of Christ is to be of the devil, to be in bondage to sin. It is to have the character of one opposed to the Lord. As Dr. R.C. Sproul writes in his commentary John: “Sin is not simply making bad choices or mistakes. Sin is having the desire in our hearts to do the will of the enemy.”