What does 'no prophecy of the Scripture is of any private interpretation' mean?
The phrase means Scripture prophecy must not be privately twisted or isolated from its context. No one should take a single verse and make it say what it does not mean. Prophecy did not originate by human will; holy men of God spoke as moved by the Holy Spirit.
Les explains that the word “knowing” in this passage is emphatic in the Greek—not a casual acceptance, but a bona fide knowledge without doubt or question. He says “no prophecy of the Scripture is of any private interpretation” means you do not just take one verse and twist it out of shape to make it say something it does not say. Instead, you leave everything in its context. He adds that no Scripture is of private interpretation, and the reason is given in verse 21: prophecy did not come in old time by the will of man. The word “holy” means set apart. Holy men of God did not speak as they dreamed it up, or as they remembered what they heard around a campfire, or as something handed down from generation to generation. They spoke or wrote as they were moved or carried along by the Holy Spirit.
Knowing this first, that no prophecy of the scripture is of any private interpretation.