What did Peter mean by Paul being hard to understand?

2 Peter 3:15-16

And account that the longsuffering of our Lord is salvation; even as our beloved brother Paul also according to the wisdom given unto him hath written unto you; As also in all his epistles, speaking in them of these things; in which are some things hard to be understood, which they that are unlearned and unstable wrest, as they do also the other scriptures, unto their own destruction.

This is used by enemies of Eternal Security and of Faith Alone, and by people saying we are still under the Law to say basically that you shouldn't take those most commonly cited Paul passages at face value.

Peter said "some things", he did not say the main point that most of Paul's Epistles are all about.

 Some people will translate 2 Peter 3:17 in a way to make it seem like it uses the word Amonia or Lawless.  But this is a completely different word that I feel the KJV was correct in rendering Wickedness. So no, it doesn't help us determine what he meant by Paul being misunderstood in the prior verses.

My first instinct as a historian was to think of how the earliest Christian Gnostic, Marcion, used Paul as the basis for most of his heresy.  But Marcion lived well after Peter's time.  And think Marcion has been misrepresented by the Church Fathers.

I also think about how Paul is the most misunderstood NT writer when it comes to sexuality.  With people for hyper prudish attitudes quoting Paul the most, and those who don't believe The Bible agrees with itself often saying Paul and Paul alone of NT writers supports Plato's sexual morality.  All of the NT clobber passages are form Paul.  Yet I feel I have shown elsewhere that Paul isn't the prude people think he is.

But..... Let's use Scripture to interpret Scripture, and keep our personal biases out of this.

Acts deals with Paul being accused of saying things he didn't say, but those are accusations of unbeleivers, Peter is alluding to misunderstandings within The Church.

This is from 2nd Peter not 1st Peter.  This is Peter's eschatological epistle, especially chapter 3 which this ends.  He's warning of deceptions in the end days that we need to be prepared for.

I agree with those scholars who say contrary to the titles we've given them that 2nd Peter was actually written well before first Peter.  That best explains why First Peter is more polished in it's use of Greek (something skeptics use to assert they can't have same author).

1 Thessalonians is generally believed to be among Paul's earliest Epistles, so could it be 2nd Peter was written between the Thessalonians Epistles?

Because in II Thessalonians 2 is where Paul himself refers to people misusing what he had to say.  Now I often see it claimed verse 2 refers to a letter forged in Paul's name.  But I disagree, the context here is clearly about a misunderstanding on what he said in I Thessalonians 4.

You see I find Pre-Trib commentaries on II Thessalonians 2 hilarious because that chapter is all about refuting Pre-Trib's imminence doctrine.  I had covered this in the very first post of this blog.  (Disclaimer however, since that first post I've changed my position on Dispensationalism.)  But this is also why I don't agree with attacking Pre-Trib by saying it didn't exist before Darby, because this misunderstanding was one Paula addressed while he lived.

And today many Pre-Tribbers will argue only Paul talks abut the Rapture, they'll misuse his Mystery statement to assert that you won't find it taught in the Olvite Discourses or Revelation or any of the Prophets of the Hebrew Bible.  And 1 Corinthians 15 is the sole basis for the Secret Rapture doctrine.

So that is most likely the issue Peter had in mind.