of Sarah was reasonable; and Abraham was compelled to recognise in her demand the voice of God (vv. 10-12). The two boys, like Esau and Jacob in the next generation, represented opposite principles and ways of life, whose counterworking was to run through the course of future history. Their incompatibility was already manifest. [126] Kalisch, _Commentary_, on Genesis xxi. 9. The Apostle's comparison must have been mortifying in the extreme to the Judaists. They are told in plain terms that they are in the position of outcast Ishmael; while uncircumcised Gentiles, without a drop of Abraham's blood in their veins, have received the promise forfeited by their unbelief. Paul could not have put his conclusion in a form more unwelcome to Jewish pride. But without this radical exposure of the legalist position it was impossible for him adequately to vindicate his gospel and defend his Gentile children in the faith. II. From this contrast of birth "according to flesh" and "through promise" is deduced the opposition between _the slave-born and free-born sons_. "For these (the slave-mother and the free-woman) are two covenants, one indeed bearing children unto bondage--which is Hagar" (ver. 24). The other side of the antithesis is not formally expressed; it is obvious. Sarah the princess, Abraham's true wife, has her counterpart in the original covenant of promise renewed in Christ, and in "the Jerusalem above, which is our mother" (ver. 26). Sarah is the typical mother,[127] as Abraham is the father of the children of faith. In the _systoichia_, or tabular comparison, which the Apostle draws up after the manner of the schools, _Hagar_ and _the Mosaic covenant_, _Sinai_ and _the Jerusalem that now is_ stand in one file and "answer to" each other; _Sarah_ and _the Abrahamic covenant_, _Zion_ and _the heavenly Jerusalem_ succeed in the same order, opposite to them. "Zion" is wanting in the second file; but "Sinai and Zion" form a standing antithesis (Heb. xii. 18-22); the second is implied in the first. It was to _Zion_ that the words of Isaiah cited in ver. 27, were addressed. [127] Comp. Heb. xi. 11, 12; 1 Pet. iii. 6.