Faith is not an ethnic identity. The issue here is not who was born of Abraham, but who embraced Abraham’s faith.
On the surface, the English translations of this passage can be somewhat confusing. If these folks began believing in Jesus, why was He picking an argument with them? It’s important to understand that Jesus is sifting their hearts. To be a disciple of Jesus has certain basic requirements. It’s not enough to simply buy into His teaching, but it requires embracing the faith He teaches. He was far more than just another rabbi. Jesus flatly says that this is not a mere matter of learning His teachings.
Even the Pharisees taught that fully embracing the Covenant was the key to genuine freedom. What Jesus said about being free was offensive to some because He said His teachings were consistent with the Law, but accepting that idea would mean rejecting an awful lot of Talmudic tradition. One of their silliest Talmudic traditions was to assert that they were superior to other races. They had never been truly enslaved — which was a blatant lie. Did they forget Egypt, Assyria, Babylon, Persia and Rome? For them, having been born of Abraham meant God’s Chosen, better than all the rest of humanity. The Talmudic tradition said it was because they were inherently better, that God made them better, and now Jehovah had no choice but to keep His loyalty to them.
Jesus tried to steer the conversation back into the moral realm. The freedom He was offering was from the bondage to sin. This made them the equivalent of slaves in God’s kingdom. Slaves could be sold, as God did to Israel several times. However, the heir was not going to be kicked out of His home. If they could embrace the Son, they could inherit the blessings of His sonship.
Jesus acknowledged that they were descendants of Abraham in the conventional sense, but they weren’t acting anything like their ancestor. Some of the folks claiming to believe Him were the same people who had participated in the death warrant against Him. That’s not the way Children of Abraham are supposed to act. The Law of Moses forbade a death warrant without a proper trial. Jesus was teaching the Word of His Father in Heaven; they were pursuing the will of some other father. This went back and forth a bit, and at one point they raise the rumors of Jesus being illegitimate. The “we” was emphatic: “Well, we were not born of fornication!”
Jesus didn’t take the bait. Instead, He turned it back around. Children of God would not be arguing like this against genuine faith, and in favor of legalism. Children of God would not be picking over semantics when divine revelation came in symbolic parables. They were being obtuse. So Jesus gets quite blunt about their affinity for the path of the Devil. The Greek word John uses means the Slanderer; Jesus dares anyone to find sin in His teaching.
He cannot accept as disciples those who reject His teaching as the Word of God.