The seed of Abraham can describe the physical descendants of Abraham (singular or plural) and the spiritual descendants of Abraham—but they are all linked together and one cannot be discussed fully without invoking the others.
Who exactly are the seed of Abraham?
Physically, Abraham produced two sons—Ishmael whose lineage includes most all Arabs, and Isaac whose lineage includes the ethnic and religious Hebrews (Israelites, Jews).
However, Paul writes that only a right relationship with God can define a descendant of Abraham, spiritually speaking. "For no one is a Jew who is merely one outwardly, nor is circumcision outward and physical. But a Jew is one inwardly, and circumcision is a matter of the heart, by the Spirit, not by the letter. His praise is not from man but from God" (Romans 2:28–29).
Both John the Baptist and Jesus confronted Jewish leaders who relied upon a physical descendance from Abraham, but failed to grasp the faith relationship Abraham had with God. John called on them to repent: "Bear fruit in keeping with repentance. And do not presume to say to yourselves, 'We have Abraham as our father,' for I tell you, God is able from these stones to raise up children for Abraham" (Matthew 3:8–9).
Jesus also tried to focus the Jews of His time on a relationship with God through more than a physical lineage with Abraham. In John 8:33–59, Jews sought to kill Jesus, repeatedly establishing their connection with Abraham and therefore with God. Jesus confronts them, telling them that the true descendants of Abraham would do as He did (live by faith in God rather than by rules). Jesus reveals that He knew Abraham, then claims His divinity by exclaiming that He existed before Abraham was born (John 8:58).
Spiritually, those who believe by faith in God's Son Jesus exhibit an Abrahamic faith by which they are counted as righteous (Genesis 15:6, Hebrews 11:8–19). More directly, Galatians 3:29 says, "And if you are Christ's, then you are Abraham's offspring, heirs according to promise." See also Romans 4:11–17.
These are the plural "seed" of Abraham. Singularly, the seed is Christ, as addressed in Galatians 3:16 (in reference to Genesis 12:7). "Now the promises were made to Abraham and to his offspring. It does not say, 'And to offsprings,' referring to many, but referring to one, 'And to your offspring,' who is Christ." Paul explains that Jesus is the inheritance apart from the law that Abraham is promised. He concludes the chapter by once again delineating the difference between a physical and spiritual descendant of Abraham: "There is neither Jew nor Greek, there is neither slave nor free, there is no male and female, for you are all one in Christ Jesus. And if you are Christ's, then you are Abraham's offspring, heirs according to promise" (Galatians 3:28–29).
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