The Jews were arguing with Jesus that Abraham was their father, and thus based their deliverance on ancestry. They had traced their descent back to the Patriarchs and were smugly using their pedigree as their key to heaven. But Jesus quickly pointed out that their father Abraham had been obedient to God no matter what God had asked of him…even to offering his son Isaac as a sacrifice. So in other words, true sonship with their heavenly Father would never be defined by biology & ancestry, but only by obedience.