Acts 7:8

He gave him, Abraham, of whom he was speaking, the convenant of circumcision; of which covenant, circumcision was the sign and seal by which, on the part of Abraham and his seed it was stipulated, that they should put off all carnal affections. Begat Isaac, after the promise: so that the promises were not given for Isaac's sake, but Isaac was given for the promise sake; which made these things more fit to represent gospel grace, of which St. Stephen was preaching. The twelve patriarchs; the heads of the tribes, from whom they were denominated. Of this genealogy, see Matthew 1:1,2, &c., and the history of it in Genesis.