Galatians 3:7 “Understand, then, that those who believe are children of Abraham.”
Paul’s brevity is ingenious – in verse 6, he begins by asking the audience to “Consider Abraham,” and then in this verse he simply says “Understand” . . . He is using the very law the Judiazers rely on in order to refute their heretical concept. That is because the concept here of who are “children of Abraham” -- who REALLY are the "children of Abraham" -- is the central point of the Judiazers’ argument. Abraham was both the physical and spiritual “father” of the Jewish people. (He still has that moniker today – remember in Sunday School singing “Father Abraham . . . has many sons . . . .”). The Jews of Paul’s day relied heavily on this concept – it was very important, even vital, to recognize their genealogical connection to Abraham, as well as being spiritual sons of Abraham. (To properly focus this, I suggest looking at Jesus’ argument with the Pharisees in John 8:31-59).
This concept of being a “spiritual son” was perhaps more important. The concept of a great teacher, a rabbi, or a spiritual mentor was central to Jewish Culture in New Testament times. A person was considered a “son” of his mentor (in a spiritual sense) if he imitated him, if he excelled in righteousness, if he acted like his moral predecessors. A pious Jew would take great pride in both his ethnic connections to the community, but more so in his obedience to the principles and rules that defined the community.
Jesus refuted this concept in John 8, recognizing that the Pharisees were ethnically Jewish, but pointing out that they failed to “do the things that Abraham did.” (John 8:39) He ultimately showed them that both ethnicity and obedience were not the means to get to know God – in Luke 3:8, Jesus decried ethnicity by saying that God could make children of Abraham from stones if he so desired, and in John 8:44, he stated that the practices of the Pharisees made them the "children of the devil." Ultimately, in John 8:58, Jesus notes that because He is God, the connection to Him is what really matters!
Because of these traditional views about ethnicity and obedience which are embodied in the concept of being “children of Abraham,” Jews would have never used that term to describe a Gentile. The only way to be a “child” of Abraham was to convert to Judaism, and obey the law—that is, follow in Abraham’s spiritual footsteps, so to speak. Paul uses scripture here, from the very law of Moses the Judiazers insisted must be followed, to prove otherwise – those who BELIEVE are Abraham’s spiritual offspring. This turns Jewish tradition (at least the tradition the Judiazers thought they believed in) on its head. But again, if you connect this concept to what Jesus was arguing about in John 8 – the key is not pedigree, or obedience, or in identifying with a group (even, dare I say, a particular denomination, theological system, or church)– its in a RELATIONSHIP with a living person, indeed, the living God – the great I AM!! (See John 8:58).