But my covenant will one establish with Isaac
The covenant of circumcision; for though Ishmael was circumcised,
and his posterity practised that rite, yet it was not enjoined
them of God; nor was it to them, or served the same purpose as to
the Israelites; and particularly the promise of the land of
Canaan, made in that covenant, belonged only to the posterity of
Isaac, and to those only in the line of Jacob, and especially
that of the Messiah springing from him, which circumcision had a
respect unto:
whom Sarah shall bear unto thee, at this set time, in the
next year:
that is, at the end of nine months, which is the set time a woman
goes with child.