For the prophecy came not in old time - Margin, or, "at any." The Greek word (ποτὲ pote) will bear either construction. It would be true in either sense, but the reference is particularly to the recorded prophecies in the Old Testament. What was true of them, however, is true of all prophecy, that it is not by the will of man. The word "prophecy" here is without the article, meaning prophecy in general - all that is prophetic in the Old Testament; or, in a more general sense still, all that the prophets taught, whether relating to future events or not.
By the will of man - It was not of human origin; not discovered by the human mind. The word "will," here seems to be used in the sense of "prompting" or "suggestion;" men did not speak by their own suggestion, but as truth was brought to them by God.
But holy men of God - Pious men commissioned by God, or employed by him as his messengers to mankind.
Spake as they were moved by the Holy Ghost - Compare 2-Timothy 3:16. The Greek phrase here (ὑπὸ Πνεύματος Ἁγίου φερόμενος hupo Pneumatos Hagiou pheromenos) means "borne along, moved, influenced" by the Holy Ghost. The idea is, that in what they spake they were "carried along" by an influence from above. They moved in the case only as they were moved; they spake only as the influence of the Holy Ghost was upon them. They were no more self-moved than a vessel at sea is that is impelled by the wind; and as the progress made by the vessel is to be measured by the impulse bearing upon it, so the statements made by the prophets are to be traced to the impulse which bore upon their minds. They were not, indeed, in all respects like such a vessel, but only in regard to the fact that all they said as prophets was to be traced to the foreign influence that bore upon their minds.
There could not be, therefore, a more decided declaration than this in proof that the prophets were inspired. If the authority of Peter is admitted, his positive and explicit assertion settles the question. if this be so, also, then the point with reference to which he makes this observation is abundantly confirmed, that the prophecies demand our earnest attention, and that we should give all the heed to them which we would to a light or lamp when traveling in a dangerous way, and in a dark night. In a still more general sense, the remark here made may also be applied to the whole of the Scriptures. We are in a dark world. We see few things clearly; and all around us, on a thousand questions, there is the obscurity of midnight. By nature there is nothing to cast light on those questions, and we are perplexed, bewildered, embarrassed. The Bible is given to us to shed light on our way.
It is the only light which we have respecting the future, and though it does not give all the information which we might desire in regard to what is to come, yet it gives us sufficient light to guide us to heaven. It teaches us what it is necessary to know about God, about our duty, and about the way of salvation, in order to conduct us safely; and no one who has committed himself to its direction, has been suffered to wander finally away from the paths of salvation. It is, therefore, a duty to attend to the instructions which the Bible imparts, and to commit ourselves to its holy guidance in our journey to a better world: for soon, if we are faithful to its teachings, the light of eternity will dawn upon us, and there, amidst its cloudless splendor, we shall see as we are seen, and know as we are known; then we shall "need no candle, neither light of the sun; for the Lord God shall give us light, and we shall reign forever and ever." Compare Revelation 21:22-24; Revelation 22:5.

For the prophecy came not in old time - That is, in any former time, by the will of man - by a man's own searching, conjecture, or calculation; but holy men of God - persons separated from the world, and devoted to God's service, spake, moved by the Holy Ghost. So far were they from inventing these prophetic declarations concerning Christ, or any future event, that they were φερομενοι, carried away, out of themselves and out of the whole region, as it were, of human knowledge and conjecture, by the Holy Ghost, who, without their knowing any thing of the matter, dictated to them what to speak, and what to write; and so far above their knowledge were the words of the prophecy, that they did not even know the intent of those words, but searched what, or what manner of time the Spirit of Christ which was in them did signify, when it testified beforehand the sufferings of Christ, and the glory that should follow. See 1-Peter 1:11, 1-Peter 1:12, and the notes there.
1. As the writer of this epistle asserts that he was on the holy mount with Christ when he was transfigured, he must be either Peter, James, or John, for there was no other person present on that occasion except Moses and Elijah, in their glorious bodies. The epistle was never attributed to James nor John; but the uninterrupted current, where its Divine inspiration was granted, gave it to Peter alone. See the preface.
2. It is not unfrequent for the writers of the New Testament to draw a comparison between the Mosaic and Christian dispensations; and the comparison generally shows that, glorious as the former was, it had no glory in comparison of the glory that excelleth. St. Peter seems to touch here on the same point; the Mosaic dispensation, with all the light of prophecy by which it was illustrated, was only as a lamp shining in a dark place. There is a propriety and delicacy in this image that are not generally noticed: a lamp in the dark gives but a very small portion of light, and only to those who are very near to it; yet it always gives light enough to make itself visible, even at a great distance; though it enlightens not the space between it and the beholder, it is still literally the lamp shining in a dark place. Such was the Mosaic dispensation; it gave a little light to the Jews, but shone not to the Gentile world, any farther than to make itself visible. This is compared with the Gospel under the emblem of daybreak, and the rising of the sun. When the sun is even eighteen degrees below the horizon daybreak commences, as the rays of light begin then to diffuse themselves in our atmosphere, by which they are reflected upon the earth. By this means a whole hemisphere is enlightened, though but in a partial degree; yet this increasing every moment, as the sun approaches the horizon, prepares for the full manifestation of his resplendent orb: so the ministry of John Baptist, and the initiatory ministry of Christ himself, prepared the primitive believers for his full manifestation on the day of pentecost and afterwards. Here the sun rose in his strength, bringing light, heat, and life to all the inhabitants of the earth. So far, then, as a lantern carried in a dark night differs from and is inferior to the beneficial effects of daybreak, and the full light and heat of a meridian sun; so far was the Mosaic dispensation, in its beneficial effects, inferior to the Christian dispensation.
3. Perhaps there is scarcely any point of view in which we can consider prophecy which is so satisfactory and conclusive as that which is here stated; that is, far from inventing the subject of their own predictions, the ancient prophets did not even know the meaning of what themselves wrote. They were carried beyond themselves by the influence of the Divine Spirit, and after ages were alone to discover the object of the prophecy; and the fulfillment was to be the absolute proof that the prediction was of God, and that it was of no private invention - no discovery made by human sagacity and wisdom, but by the especial revelation of the all-wise God. This is sufficiently evident in all the prophecies which have been already fulfilled, and will be equally so in those yet to be fulfilled; the events will point out the prophecy, and the prophecy will be seen to be fulfilled in that event.

For the prophecy came not in old time by the will of man: but (p) holy men of God spake [as they were] (q) moved by the Holy Ghost.
(p) The godly interpreters and messengers.
(q) Inspired by God: their actions were in very good order, and not as the actions of the profane soothsayers, and foretellers of things to come.

For the prophecy,.... The whole Scripture, all the prophetic writings; so the Jews call the Scriptures "the prophecy" (g), by way of eminence, and from the subject matter of the sacred word:
came not in old time by the will of man; was not brought into the world at first, or in any period of time, as and when man would, according to his pleasure, and as he thought fit: neither Moses, nor David, nor Isaiah, nor Jeremiah, nor Ezekiel, nor Daniel, nor any other of the prophets, prophesied when they pleased, but when it was the will of God they should; they were stirred up to prophesy, not by any human impulse, but by a divine influence: with this agrees what R. Sangari says,
"that the speech of the prophets, when the Holy Spirit clothed them, in all their words was directed by a divine influence, and the prophet could not speak in the choice of his own words,''
or according to his will:
but holy men of God; such as he sanctified by his Spirit, and separated from the rest of men to such peculiar service; and whom he employed as public ministers of his word: for so this phrase "men", or "man of God", often signifies, 1-Samuel 2:27.
spake, as they were moved by the Holy Ghost; who illuminated their minds, gave them a knowledge of divine things, and a foresight of future ones; dictated to them what they should say or write; and moved upon them strongly, and by a secret and powerful impulse stirred them up to deliver what they did, in the name and fear of God: which shows the authority of the Scriptures, that they are the word of God, and not of men; and as such should be attended to, and received with all affection and reverence; and that the Spirit is the best interpreter of them, who first dictated them; and that they are to be the rule of our faith and practice; nor are we to expect any other, until the second coming of Christ.
(g) R. Eliahu in Adderet apud Trigland. de Sect Karaeorum, c. 10. p. 153.

came not in old time--rather, "was never at any time borne" (to us).
by the will of man--alone. Jeremiah 23:26, "prophets of the deceit of their own heart." Compare 2-Peter 3:5, "willingly."
holy--One oldest manuscript has, "men FROM God": the emissaries from God. "Holy," if read, will mean because they had the Holy Spirit.
moved--Greek, "borne" (along) as by a mighty wind: Acts 2:2, "rushing (the same Greek) wind": rapt out of themselves: still not in fanatical excitement (1-Corinthians 14:32). The Hebrew "nabi," "prophet," meant an announcer or interpreter of God: he, as God's spokesman, interpreted not his own "private" will or thought, but God's "Man of the Spirit" (Hosea 9:7, Margin). "Thou testifiedst by Thy Spirit in Thy prophets." "Seer," on the other hand, refers to the mode of receiving the communications from God, rather than to the utterance of them to others. "Spake" implies that, both in its original oral announcement, and now even when in writing, it has been always, and is, the living voice of God speaking to us through His inspired servants. Greek, "borne (along)" forms a beautiful antithesis to "was borne." They were passive, rather than active instruments. The Old Testament prophets primarily, but including also all the inspired penmen, whether of the New or Old Testament (2-Peter 3:2).

For prophecy came not of old by the will of man - Of any mere man whatever. But the holy men of God - Devoted to him, and set apart by him for that purpose, spake and wrote. Being moved - Literally, carried. They were purely passive therein.