Jesus' opponents repeatedly appeal to Abraham as their father. Jesus does not deny their biological descent; instead he asks whether their actions resemble Abraham's.
The argument draws on an ancient expectation that children represent the character and honor of their household.
Kinship was a primary source of identity in the ancient Mediterranean world. Descent from an honored ancestor carried status, but family identity also implied loyalty and resemblance. Biblical language itself can use 'sons' or 'children' for those who share a person's character or behavior, not only genetic descent.
Jesus argues that Abraham responded faithfully to God, whereas people seeking to kill the one who speaks God's truth are acting unlike him.
The social background explains why the debate becomes so intense. Jesus is not discussing genealogy as an abstract fact; he is challenging an honor claim central to his hearers' identity.
John's distinction is important: physical descent from Abraham is acknowledged, yet spiritual resemblance is tested by the response to God's revelation.