“Knowing this first, that no prophecy of the scripture is of any private interpretation.”
King James Version (KJV)
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.
2Pe 1:20 Knowing this first. This is a reason for giving heed to the word of prophecy. That no prophecy of the scripture is of any private interpretation. Is not an interpretation of the knowledge and feelings of the prophet, but of the will of God. The next verse shows that this is the meaning.