{The same are sons of Abraham} (houtoi huioi eisin
Abraham). "These are." This is Paul's astounding doctrine to
Jews that the real sons of Abraham are those who believe as he
did, "they which be of faith" (hoi ek piste(9373)), a common idiom
with Paul for this idea (verse  9  Ro 3:26  4:16  14:23 ), those
whose spiritual sonship springs out of (ek) faith, not out of
blood. John the Baptist denounced the Pharisees and Sadducees as
vipers though descendants of Abraham ( Mt 3:7  Lu 3:7 ) and Jesus
termed the Pharisees children of the devil and not spiritual
children of Abraham (not children of God) in  Joh 8:37-44 .