For the prophecy came not in old time by the will of man: but holy men of God spake as they were moved by the Holy Ghost [2 Pet. 1:21].

“For the prophecy came not in old time by the will of man.” Obviously he is referring to Old Testament prophecy. It didn’t come by the will of man. That is, Isaiah, for example, did not sit down saying, “I think I’ll write a book because I need some money. I’ll send it to the publisher, and he will send me an advance check, and then I’ll get royalties for it.” That is the reason some men write in our day, but that is not the way Isaiah did it. Listen to Peter: “For the prophecy came not in old time by the will of man.” The prophecy of Isaiah was not something that Isaiah thought up.
“But holy men of God spake as they were moved by the Holy Ghost.” “Holy men” does not mean that the writers were some superduper saints. It means holy in the sense of being set apart for this particular office. If you are a holy Christian, it means that you are set apart for Jesus Christ. Holy means “to be set apart.”
“As they were moved by the Holy Ghost [Spirit]” is a delightful figure of speech. The Greek actually portrays the idea of a sailing vessel. The wind gets into those great sails, bellies them out, and moves the ship along. That is the way the Holy Spirit moved these men.
Here in California we have a yacht regatta each year. The yachts line up and start for Honolulu, Hawaii, to sail in around Diamond Head. (A man must be rich enough to own such a sailing yacht and to have the time to enter such a regatta.) Some time ago a doctor performed an operation on me one day, and the next day he was off sailing to Honolulu! When he got back, I was asking him about it. He told me that they have an extra sail which they put out when they get a good wind and that moves the boat right along. Well, this is exactly what Peter is saying in this verse of Scripture. These men who were set apart for the writing of the Scriptures were moved along by the Spirit of God.
Now let me remind you that this is Peter’s swan song, and, like Paul in his swan song, he emphasizes the importance of the Word of God for the days of apostasy. Paul said, “All scripture is given by inspiration of God …” (2 Tim. 3:16), and Peter is saying that the writers of Scripture were moved along by the Holy Spirit. The thought is the same. It is wonderful to see how God could take each man and use him, without changing his style or interfering with his personality, to write His Word so that His message comes across. While Paul the apostle wrote eloquent Greek, Peter the apostle—since he was a fisherman and Greek was his second language—wrote Greek that was not quite as good. Yet God used both of these men to write exactly what He wanted to say—so much so that, if God spoke out of heaven today, He would have to repeat Himself, because He already has said all that He has to say to mankind. God has gotten His Word to us through men of different personalities and different skills. For this reason I call it a man–book and a God–book.
The written Word, like the Lord Jesus, the living Word, is both human and divine. The Lord Jesus could weep at a grave, but He could also raise the dead. He could sit down at a well because He was tired and thirsty, but He could also give the water of life to a poor sinner. He could go to sleep in a boat, but He could also still the storm. He was a man, but He was God also. And the Bible is both human and divine.
Simon Peter is telling us that we have “a more sure word of prophecy.” He puts a sure rock under our feet. The Scriptures are something that we can have confidence in. No wonder the Word of God has been attacked more than anything else. If the enemy can get rid of the foundation, he knows that the building will come crashing down.
It is sheer nonsense for a preacher to stand at a pulpit and preach a sermon showing that he does not believe that the Bible is the Word of God. That, to my judgment, is as silly as the poor fellow in the insane asylum whom a visitor saw using a pickax on the foundation at the corner of the dormitory in an attempt to destroy the foundation. The visitor, wanting to be sympathetic, asked the man with the pickax, “What are you doing?”
“I’m digging away the foundation. Can’t you see?”
“Yes, but don’t you live in this building?”
“Of course I do, but I live upstairs.”
For a preacher to discredit the Word of God is equally as insane. My friend, the Scriptures as we have them are a solid foundation on which to rest our faith.
The last time I was in Greece, I went again to the Acropolis in Athens and examined the Parthenon. I have examined it several times to make sure I am accurate in this statement: there are not two parallel lines in the place, nor is there a straight line. If you go to one end and look down, you will see that it comes up to a hump in the middle and then goes back down. The Greeks had learned that the human eye never sees anything straight which is straight. This, I believe, is the reason God says that we are to walk by faith and not by sight. We can’t trust our own eyes nor our own ears, but we can rest upon the Word of God.
One of the greatest proofs that the Bible is indeed the Word is fulfilled prophecy. Over one–third of the Scripture was prophetic at the time it was first written. It is not to be treated as speculation or superstition because of the fact that a great deal of it has already been literally fulfilled. As someone has well said, “Prophecy is the mold into which history is poured.” Fulfilled prophecy is, to me, one of the great proofs of the accuracy of Scripture. Peter has said, “We have also a more sure word of prophecy.” Since one–fourth of prophecy has been fulfilled, this means that one–fourth of one–third of the Bible is fulfilled prophecy. Man cannot guess that accurately! There were three hundred thirty prophecies in the Old Testament concerning the first coming of Christ, and all of them were literally fulfilled. No human being can guess like that.
Let me give you an example. Suppose that right now I should make a prophecy that it is going to rain tomorrow. I’d have a 50 percent chance of being right, because it either will or it won’t. But suppose I add to that the prediction that it would start raining tomorrow morning at nine o’clock. That would be another uncertain element. I am no mathematician, but it seems to me that this would reduce my chance of being right by another 50 percent. Now suppose that I not only say it is going to start raining at nine o’clock but also that it will stop raining at two o’clock. According to my figuring, that would bring down my chance of being correct to 12½ percent. And it would be a lot less than that if you figure it according to a twenty–four hour day. But suppose I add three hundred uncertain elements. I would not have a ghost of a chance of being accurate. Yet the Word of God hit it, my friend. It is accurate. The Bible has moved into the area of absolute impossibility, and that to me is absolute proof that it is the Word of God.  McGee, J. V. (1991). Thru the Bible commentary: The Epistles (2 Peter) (electronic ed., Vol. 55, pp. 39–42). Nashville: Thomas Nelson.

1:21 by the will of man. As Scripture is not of human origin, neither is it the result of human will. The emphasis in the phrase is that no part of Scripture was ever at any time produced because men wanted it so. The Bible is not the product of human effort. The prophets, in fact, sometimes wrote what they could not fully understand (1 Pet. 1:10, 11), but were nonetheless faithful to write what God revealed to them. moved by the Holy Spirit. Grammatically, this means that they were continually carried or borne along by the Spirit of God (cf. Luke 1:70; Acts 27:15, 17). The Holy Spirit thus is the divine author and originator, the producer of the Scriptures. In the OT alone, the human writers refer to their writings as the words of God over 3800 times (e.g., Jer. 1:4; cf. 3:2; Rom. 3:2; 1 Cor. 2:10). Though the human writers of Scripture were active rather than passive in the process of writing Scripture, God the Holy Spirit superintended them so that, using their own individual personalities, thought processes, and vocabulary, they composed and recorded without error the exact words God wanted written. The original copies of Scripture are therefore inspired, i.e., God-breathed (cf. 2 Tim. 3:16) and inerrant, i.e., without error (John 10:34, 35; 17:17; Titus 1:2). Peter defined the process of inspiration which created an inerrant original text (cf. Prov. 30:5; 1 Cor. 14:36; 1 Thess. 2:13). MacArthur, J., Jr. (Ed.). (1997). The MacArthur Study Bible (electronic ed., p. 1954). Nashville, TN: Word Pub.