But he who was of the bondwoman was born after the flesh; but he of the freewoman was by promise.
But. The two sons, though sprung from a common father, Abraham, were, notwithstanding, very different.
After the flesh (implying weakness) - born in the usual course of nature; in contrast to Isaac, born 'by virtue of the promise' (Greek), as the efficient cause of Sarah's supernatural pregnancy (Romans 4:19). Abraham was to lay aside all confidence in the flesh (after which Ishmael was born), and to live by faith alone in the promise (according to which Isaac was miraculously born, contrary to all fleshly calculations).