I Corinthians 14:37: If any man think himself to be a prophet, or spiritual, let him acknowledge that the things that I write unto you are the commandments of the Lord.
I Thessalonians 4:2: For ye know what commandments we gave you by the Lord Jesus.
Faith alone in Christ is FULL and COMPLETE justification for our salvation: Gal. 2:16 and 3:26. Inside Gal. 3:26, God reckons, counts us, all as children of God by faith in Christ.
Galatians 2:16: Knowing that a man is not justified by the works of the law, but by the faith of Jesus Christ, even we have believed in Jesus Christ, that we might be justified by the faith of Christ, and not by the works of the law: for by the works of the law shall no flesh be justified.
Galatians 3:26: For ye are all the children of God by faith in Christ Jesus.
Since God reckons us all as children of God by faith in Christ, it cannot get any simpler than that Scripture.
Now if we consider the Word of God, we must consider all these as the Words of God (I Cor. 14:37, I Thess 4:2, Gal. 2:16 and 3:26) which were DIRECTLY REVEALED to our Apostle Paul to write unto you regarding for today the new commandments of the Lord Jesus Christ (I Cor. 14:37, I Thess 4:2). Failing to receive these commandments from the Lord Jesus Christ and to recognize that the epistles have grace commandments from the Lord Jesus Christ, will be turn out to destruction, exactly what Peter wrote about people or religious organization that reject these things -
II Peter 3:15: 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;
II Peter 3:16: 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.
If someone fights against these, as Peter so revealed, then they also fight against God and His Words in the entire Bible, but especially in God's epistles - which they that are unlearned and unstable wrest, as they do also the other scriptures, unto their own destruction.
Seems pretty clear to me. Peter was a concrete speaker/writer.