NOTES for Joh 8:31-42
All Jews consider themselves "children of Abraham," and every believing Jew is ready to declare loyalty to Moses. So it was in Gospel times, and before that, before Christ came into the world, and today nothing has changed in this respect in Jewish self-understanding. But Jesus seems to call into question things that are obvious to every Jew. He speaks of slavery, and they answer Him that the children of Abraham have never been slaves to anyone.
The point here is not only that Israel really never knew slavery in its classical, Greco-Roman or Egyptian, form, but that everyone who is faithful to the God of Abraham and the Torah of Moses is free by definition. "We are God's children; we are not children of fornication," the people listening to Jesus tell Him. And the point is not that immorality was in principle unknown to Israel (unfortunately, that is far from true), but that everyone who belongs to the people of God is a spiritual child of the God to whom he belongs from birth.
But Jesus is speaking about something else. He has in mind not the external, religious side of the matter, but its spiritual essence. You have no slavery, you are not slaves; but if you are slaves of sin, what freedom can one speak of? You say about yourselves that you are children of Abraham. But Abraham knew how to listen to God and hear Him; he did not place customs and traditions dear to the heart above the word of God, above revelation. And you? You say that your Father is God, Jesus says to His listeners, but He is My Father too; so why do you accept neither Me nor what I say? After all, you have had many chances to be convinced that I came from God. So what then?
The people listening to Jesus have nothing to answer to these questions. And they continue to accuse and doubt. This is what people often do when they have no answer on the substance.