2 Peter 1:20 ‘No prophecy of scripture ever comes about by the prophet’s own imagination.’

This passage may mean,

(a) no prophecy is to be understood by private interpretation; i.e. it must be interpreted as the Church understands it, or as the Holy Spirit illuminates it.  This would be consistent with the fact that the false teachers certainly did misinterpret Scripture (2 Pet 2:1; 3:16).

According to Bauckham, most commentators and translations adopt this interpretation.  These include the REB.

According to The Second Helvetic Confession:

‘The apostle Peter has said that the Holy Scriptures are not of private interpretation, (2 Pet 1:20) and thus we do not allow all possible interpretations…Wherefore we do not despise the interpretations of the holy Greek and Latin fathers, nor reject their disputations and treatises concerning sacred matters as far as they agree with the Scriptures: but we modestly dissent from them when they are found to set down things differing from, or altogether contrary to the Scriptures…We do not permit ourselves, in controversies about religion or matters of faith, to urge our case with only the opinions of the fathers or decrees of councils; much less by received customs, or by the large number of those who share the same opinion, or by the prescription of a long time. Who is the Judge? Therefore, we do not admit any other judge than God himself, who proclaims by the Holy Scriptures what is true, what is false, what is to be followed, or what is to be avoided. So we do assent to the judgments of spiritual men which are drawn from the Word of God. Certainly Jeremiah and other prophets vehemently condemned the assemblies of priests which were set up against the law of God; and diligently admonished us that we should not listen to the fathers, or tread in their path who, walking in their own inventions, swerved from the law of God.’

Robert Traill, while acknowledging that this is a ‘dark place’, thinks it means that

‘no man applies the scripture well, that applies it to one person, or to one time: for it was designed for common public good to all who read it, to the ends of the world.’  (Works, Vol IV).

(b) no prophecy arises from the prophet’s own understanding; i.e. it is from God.

Green writes:

‘Peter…is talking about the divine origin of Scripture, not about its proper interpretation’.

Towner agrees:

‘Peter is affirming the divine origin of Scripture, not considering here who may interpret Scripture.’

Gundry (Commentary on the New Testament);

‘Peter isn’t referring to the interpretation of prophecy. He’s referring to prophecy as interpretation, the interpretation of past, present, and future events.’

Moo also agrees, but judges the decision to be finely balanced:

‘An emphasis on the origin of prophecy fits well with Peter’s concern in verse 19 to get his readers to pay closer attention to prophecy. But a reminder that prophecy is not a matter of private interpretation would make a fitting response to the false teachers, who were probably twisting Scripture to suit their own purposes.’

This interpretation is also supported by Calvin.

The prophets did not invent their messages, but spoke the word of the Lord. This in contrast to the false prophets, Jer 23:16. ‘This is what the LORD Almighty says: “Do not listen to what the prophets are prophesying to you; they fill you with false hopes. They speak visions from their own minds, not from the mouth of the LORD.’

See also Jer 14:14; Ezek 13:3.

MacLeod, A Faith to Live By, writes:

‘These men were not simply giving their own opinions: not even their own expert opinions. Nor did prophecy come ‘by the will of man’. (2 Pet 1:21) It wasn’t a case of a man saying, ‘I’m going to prophesy.’ The initiative did not lie with man at all. You see that so often with regard to such figures as Moses and Jeremiah and Jonah. We can almost say of them that they were dragged kicking into this particular ministry. It wasn’t their own choice. And when they spoke, the message they proclaimed wasn’t from themselves at all.’

At the close of a lengthy discussion, Bauckham paraphrases what he considers to be the true meaning:

‘No prophecy in the OT Scriptures originated from human initiative or imagination. The Holy Spirit of God inspired not only the prophets’ dreams and visions, but also their interpretations of them, so that when they spoke the prophecies recorded in Scripture they were spokesmen for God himself.’

This second view the more likely, since the whole issue in this passage is about authenticity, not interpretation.