In Lost Scriptures, Books that Did Not Make It into the New Testament, Bart D Ehrman writes on the Letter of Peter to James:
"The Letter of Peter to James" is one of a number of early Christian writings pseudonymously written in the name of Jesus' disciple, Simon Peter... It does not survive as an independently transmitted letter, but only as the preface to the "Homilies of Clement" a collection of legendary stories and sermons of Clement of Rome ...
The Letter of Peter urges James to pass along the accompanying sermons carefully to those who are worthy to receive them, and to no one else.
The clear concern is that Peter's teachings not be corrupted by those who have a different understanding of the truth. Both the Letter and the Reception are Jewish Christian in their orientation, as seen in their emphasis on emulating the actions of Moses, on keeping the Law, and on opposing the person Peter calls "the man who is my enemy." Peter's opponent here is commonly understood to be none other than the apostle Paul ( Gal 2:11-14) who taught that salvation comes to all people, Jew and Gentile, apart from following the Law of Moses, and who urged Gentiles not to be circumcised (Gal. 5:2-12)."
Verse 5: "For to do such a thing means to act contrary to the law of God which was made known by Moses and was confirmed by our Lord in its everlasting continuance. For he said: "The heaven and the earth will pass away, but one jot or one title shall not pass from the law.
Verse 6: "This he said that everything might come to pass. But those persons who, I known not how, allege that they are at home in my thoughts wish to expound the words which they have heard of me better than I myself who spoke them. To those whom they instruct they say that this is my opinion, to which indeed I never gave a thought.
Verse 7: "But if they falsely assert such a thing while I am still alive, how much more after my death will those who come later venture to do so?"
Chapter 2 verse 3: "For some from among the Gentiles have rejected my lawful preaching and have preferred a lawless and absurd doctrine of the man who is my enemy.
Verse 4: "And indeed some have attempted, whilst I am still alive, to distort my words by interpretations of many sorts, as if I taught the dissolution of the law and, although I was of this opinion, did not express it openly. But that may God forbid!