By faith Abraham, when he was called to go out into a place which he should after receive for an inheritance, obeyed (literally, when called, obeyed to go out, etc); and he went out, not knowing whither he went. The reference is to the first call of Abraham (Genesis 12:1), his obedience to which is the first instance of the faith which the whole life of the father of the faithful so eminently exemplifies. The fact of the place he was to go to being so far unrevealed (intimated only as "a land that I will show thee") enhances the faith displayed, He followed the Divine voice as it were blindly, not seeing whither it was leading him, knowing only that it was right to follow it. So to those who walk by faith now the future may be unknown or dim.
"Lead thou me on.
... I do not ask to see
The distant scene;
one step enough for me."
By faith he sojourned in (rather, went to sojourn in) the land of promise, as in a strange country (literally, as one belonging to others; i.e. not his own; "As in an alien land" (Wickliffe); cf. Genesis 23:4, "I am a stranger and sojourner with you"), dwelling in tabernacles with Isaac and Jacob, the heirs with him of the same promise: for he looked for a city which hath foundations (literally, the foundations) whose Builder and Maker is God. Of course, here, "with Isaac and Jacob" means "as did also Isaac and Jacob." The three successive patriarchs are presented in Scripture as representing the period of nomadic life in the land of promise, not yet possessed; alike supported by faith in the Divine word; and hence they are ever grouped together (of. Genesis 28:13; Genesis 32:9; Genesis 48:15;Genesis 1:1-31. 24; Exodus 3:6; Deuteronomy 9:5; 1 Kings 18:36, etc; also Matthew 22:32; Luke 13:28). The meaning of their history to us, and the object of their common hope, are further set forth in Genesis 23:13-17, and will be under them considered. In the mean time an instance of Abraham's faith, peculiar to himself, is adduced.
By faith also Sarah herself received strength to conceive seed, even when she was past age, because she judged him faithful who had promised. Therefore sprang there even of one, and him as good as dead, so many as the stars of the sky in multitude, and as the sand which is by the sea-shore innumerable. The vitality of Abraham's faith is represented as evinced by its surviving and triumphing over a succession of trials, over apparent impossibilities. One such peculiar trial was the long delay of the birth of a legitimate heir through whom the promise of an innumerable seed might be fulfilled, and this till it seemed out of the question in the natural course of things. Yet "he staggered not at the promise of God through unbelief … being fully persuaded that what he had promised he was able to perform" (see Romans 4:17-23, which is a fuller statement of the idea of this verse, including the use of the words νενεκρώμενον and νέκρωσις to express effeteness, and ἐδυναμώθη, corresponding to δύναμον ἔλαβε here. This is a further instance of Pauline thought in this Epistle—ideas already enlarged on by St. Paul being taken for granted as understood) In Romans Abraham's faith in this regard is treated as typifying Christian faith in the resurrection from the dead (verse 24), as is also, in the chapter before us (verse 19), his faith displayed on the occasion of the offering of Isaac. For to us also our inability to conceive the mode of accomplishment of what well-grounded faith assures us of is no just cause for staggering. "How are the dead raised up? and with what kind of body do they come?" was asked by the Corinthian doubters. St. Paul directs them, in reply, to faith in "the power of God" to accomplish his purposes and fulfill his promises in ways unknown to us, transcending, though analogous to, the mysterious processes of nature that we see before our eyes. For "with God all things are possible." Sarah is here joined with Abraham, as also "receiving power" by faith, i.e. her own faith, as the structure of verse 11 seems evidently to imply. But how is this consistent with the account of her in Genesis, where she is nowhere held up as an example of faith; nay, is censured for incredulity (Genesis 18:12-16) with respect to the promise cf. offspring? The answer may be that her temporary unbelief is concluded to have been succeeded by faith, as proved by the result, viz. that she "received power." And, indeed, her laughter recorded in Genesis 18:1-33, does not seem intended to imply any permanent "heart of unbelief;" for even Abraham had laughed as she did when the same announcement had been previously made to him (Genesis 17:17), and the "laughter" associated with her memory has quite a different meaning given it when that of temporary incredulity was changed into that of joy on the birth of the promised son, who was consequently called Isaac (equivalent to "laughter"). It is, however, Abraham himself who is put prominently before us as the great example of faith; Sarah is only introduced by his side (with the words καὶ αὐτὴ) as sharing it and cooperating to the result. To him singly the writer returns in Genesis 18:12, διὸ καὶ ἀφ ἑνὸς, etc.