Hebrews 11:18

18. Of whom--rather as Greek "He (Abraham, not Isaac) TO whom it was said" [Alford]. Bengel supports English Version. So He 1:7 uses the same Greek preposition, "unto," for "in respect to," or "of." This verse gives a definition of the "only-begotten Son" (He 11:17). in Isaac shall thy seed be called--(Ge 21:12). The posterity of Isaac alone shall be accounted as the seed of Abraham, which is the heir of the promises (Ro 9:7).

Robert Jamieson, A. R. Fausset & David Brown, 1871 · public domain

Verse 18. Of whom it was said, That in Isaac shall thy seed be called. Gen 21:12. A numerous posterity had been promised to him. It was there said expressly that this promise was not to be fulfilled through the son of Abraham by the bond-woman Hagar, but through Isaac. Of course, it was implied that Isaac was to reach manhood; and yet, notwithstanding this, and notwithstanding Abraham fully believed it, he prepared deliberately, in obedience to the Divine command, to put him to death. The phrase, "thy seed be called," means, that his posterity was to be named after Isaac, or was to descend only from him. The word "called," in the Scriptures, is often equivalent to the verb to be. See Isa 56:7. To name or call a thing, was the same as to say that it was, or that it existed. It does not mean here that his spiritual children were to be called or selected from among the posterity of Isaac, but that the posterity promised to Abraham would descend neither from Ishmael nor the sons of Keturah, but in the line of Isaac. This is a strong circumstance insisted on by the apostle, to show the strength of Abraham's faith. It was shown not only by his willingness to offer up the child of his old age--his only son by his beloved wife, but by his readiness, at the command of God, to sacrifice even him on whom the fulfilment of the promises depended.

(1) "Of whom" "To" (d) "That in Isaac" Gen 21:12

Albert Barnes, 1834 · public domain