Hebrews 11:12

Wherefore also there sprang of one, and him as good as dead, so many as the stars of heaven in multitude, and as the sand which is by the seashore, innumerable.

And him as good as dead indicates that not merely Sarah, but Abraham also, was past the time of life when any children might have been expected of him; and although God, true to his promise, gave them strength for the birth of Isaac, it was plainly through the intervention of the divine will. If that was the case, the question arises, how then could Abraham have later married Keturah and have fathered by her numerous sons (Genesis 25)? The explanation is that Moses, in giving a history of Keturah and her sons, did not do so chronologically; but, as the best historians do, he dealt with the primary line of Isaac first, though Isaac was the last of Abraham's sons. Keturah was probably one of the many concubines that Abraham owned.

Abraham was a wealthy oriental patriarch who already had "three hundred eighteen servants" born in his own house (Genesis 14:14), as early in his career as the rescue of Lot; and since those were not Sarah's children, they must have belonged to his concubines. Some commentators, notably Hallet, think Keturah was among the souls "they had gotten in Haran" (Genesis 12:5); and it has been suggested that Keturah was the mother of Eliezar (Genesis 15:2,3), the apparent heir of Abraham for many years, suggesting that Eliezar was the oldest of the sons of the concubines. The number of concubines, though not given, was certainly plural (Genesis 25:6). The events relative to Hagar do not contradict the above view. Sarah, earnestly desiring a child, did not desire one by any of Abraham's concubines, as they were viewed as Abraham's servants, not hers; it was thus something different when she proposed that Abraham beget a child by her maid, Hagar, which would thus give her a child she could emotionally identify with, as being hers. There is an element of speculation in this explanation; but surely it is preferable to the supposition that when God rejuvenated Abraham for the birth of Isaac, he revived his powers for such a long while afterward. If the latter had been the case, why did it not also occur in the case of Sarah and permit her to bear other children in addition to Isaac? In view of all this, it would seem that Hallet's view of the problem is correct; and to this also agrees the comment of Macknight.[20]

Stars of heaven in multitude ... innumerable represents that Abraham's posterity should be innumerable, a prophecy which, of course, has come to pass. The holy writer's making the sands of the seashore an example of HOW innumerable Abraham's seed should be is easily understood; but it is amazing that he should also have pressed "the stars of heaven" into the comparison, since, for ages, people had believed the stars to be numerable and, in fact, comprising only five or ten thousand, or some such number, in the ancient view. It must, then, have been by divine inspiration that the author of Hebrews understood the number of stars as unlimited at such a long time before the invention of the telescope disclosed such to be indeed the truth. Modern astronomy has indeed shown the number of stars to be beyond all human calculation, their numbers being reckoned in terms of billions of billions, with countless other billions lying beyond the range of the most powerful telescopes. This suggests another bit of astronomical information provided by Paul's statement that "one star differeth from another star in glory" (1 Corinthians 15:41), a revealed truth far in advance of the modern astronomy which has so astoundingly confirmed it.