Please read this quote in context.. It is about the Infallibility of scripture. ALL scripture is prophetic and is not the word of men.. THAT is what that is what Peter saying IN CONTEXT.
From Jamieson-Fausset-Brown Bible Commentary
First-the foremost consideration in studying the word of prophecy. Laying it down as a first principle never to be lost sight of.
is-Greek, not the simple verb, to be, but to begin to be, "proves to be," "becometh." No prophecy is found to be the result of "private (the mere individual writer's uninspired) interpretation" (solution), and so origination. The Greek noun epilusis, does not mean in itself origination; but that which the sacred writer could not always fully interpret, though being the speaker or writer (as 1Pe 1:10-12 implies), was plainly not of his own, but of God's disclosure, origination, and inspiration, as Peter proceeds to add, "But holy men . spake (and afterwards wrote) . moved by the Holy Ghost": a reason why ye should "give" all "heed" to it. The parallelism to 2Pe 1:16 shows that "private interpretation," contrasted with "moved by the Holy Ghost," here answers to "fables devised by (human) wisdom," contrasted with "we were eye-witnesses of His majesty," as attested by the "voice from God." The words of the prophetical (and so of all) Scripture writers were not mere words of the individuals, and therefore to be interpreted by them, but of "the Holy Ghost" by whom they were "moved." "Private" is explainec
Wesley
1:20 Ye do well, as knowing this, that no scripture prophecy is of private interpretation - It is not any man's own word. It is God, not the prophet himself, who thereby interprets things till then unknown.
The Youngs LITERAL greek interpretation says this
Young's Literal Translation this first knowing, that no prophecy of the Writing doth come of private exposition,
That is why the scripture clearly teaches us that the word of God is foolishness to those that are perishing ...correct exposition is essential