Look now toward heaven - It appears that this whole transaction took place in the evening; see on Genesis 13:14 (note). Abram had either two visions, that recorded in Genesis 15:1, and that in Genesis 15:12, etc.; or what is mentioned in the beginning of this chapter is a part of the occurrences which took place after the sacrifice mentioned Genesis 15:9, etc.: but it is more likely that there was a vision of that kind already described, and afterwards a second, in which he received the revelation mentioned Genesis 15:13-16. After the first vision he is brought forth abroad to see if he can number the stars; and as he finds this impossible, he is assured that as they are to him innumerable, so shall his posterity be; and that all should spring from one who should proceed from his own bowels - one who should be his own legitimate child.

And he brought him forth abroad,.... Out of his tent into the open air, which was done through his call, and at his direction; or by an impulse upon his mind; or this might not be real and local, only vision:
and said, look now towards heaven; either with his bodily eyes, or with the eyes of his mind:
and tell the stars, if thou be able to number them; this looks as if it were in a vision that this was said to him, and what follows done in the day, since it was in the daytime, before the sun was set, Genesis 15:12, when the stars could not be seen; and therefore were represented to his mind, and he was directed to consider them in it, whether they could be numbered by him or not: but this might be in the preceding night, or early in the morning, before the sun arose, that Abram was directed to go out of his tent, and view the heavens, and the multitude of stars in them, and try if he could number them; and he might be employed all the day following till sunset, in preparing the creatures for the sacrifice, in cutting them asunder, laying their pieces in order, and watching them, and driving the fowls from them. The multitude of his seed is before signified by the dust of the earth, which cannot be numbered, Genesis 13:16, and here by the stars of the sky innumerable; as they are to man, though not to God: some have pretended to number them, as Aratus, Eudoxus, and Hipparchus, among the ancients, and also modern astronomers; but then they are such only that are visible to the eye, and in one hemisphere, and their accounts are very various; whereas there are multitudes to be discerned by glasses, and some not to be distinguished, as in the galaxy, or milky way, and others in the other hemisphere. Now Abram here is bid to try what he could do, and this was in his own way; for he is said by many Heathen writers (h) to be famous for arithmetic and astrology, or astronomy; but as great a master as he was in these sciences, be was not able to number the stars, which is here plainly intimated, since it follows:
and he said, so shall thy seed be: as innumerable as the stars, as they were, even his natural seed, Hebrews 11:12; and especially his spiritual seed, who have the same kind of faith he had, and as they will be in the latter day particularly, Hosea 1:10.
(h) Apud Euseb. ut supra, (Evangel. Praepar.) l. 9. c. 16, 17. Orpheus apud Clement. Stromat. l. 5. p. 607.

And he brought him forth - It seems, early in the morning, and said, look now toward heaven, and tell the stars: so shall thy seed be - So innumerable, for so the stars seem to a common eye. Abram feared he should have no child at all, but God tells him his descendents should be so many as not to be numbered. So illustrious, as the stars of heaven for splendour; for to them pertained the glory, Romans 9:4. Abram's seed according to the flesh were like the dust of the earth, Genesis 13:16, but his spiritual seed are like the stars of heaven.