For it is written, that Abraham had two sons, the one by a bondmaid, the other by a freewoman.
(Genesis 16:3-16; Genesis 21:2.)
Abraham - whose sons ye wish to be (cf. Romans 9:7-9).
A bond maid, the other by a free woman - Greek 'the well-known bond maid the free woman ' A bond maid, the other by a free woman - Greek, 'the well-known bond maid ... the free woman.'