The Apostle Paul wrote, in 1 Corinthians 2:13, "we speak, not in the words which man's wisdom teacheth, but which the Holy Ghost teacheth; comparing spiritual things with spiritual." What then are "spiritual things?" Well, the bible tells us that spiritual things are words. Jesus said, in John 6:63. "the words that I speak unto you, they are spirit, and they are life." With that in mind, let's just compare some spiritual things, comparing words with words, spiritual things with spiritual.
What Jesus said on the earth:
(Mat 6:14 KJV) For if ye forgive men their trespasses, your heavenly Father will also forgive you:
(Mat 6:15 KJV) But if ye forgive not men their trespasses, neither will your Father forgive your trespasses.
According to that passage then, in the earthly ministry of Christ, as he went about teaching in all their synagogues and preaching the gospel of the Kingdom, he taught that their forgiveness would be based on something they did. In other words, based on their forgiving other men. This doctrine was a part of the gospel of the Kingdom which was preached at that time.
What the risen Christ said through Paul:
(Col 2:10 KJV) And ye are complete in him, which is the head of all principality and power:
(Col 2:11 KJV) In whom also ye are circumcised with the circumcision made without hands, in putting off the body of the sins of the flesh by the circumcision of Christ:
(Col 2:12 KJV) Buried with him in baptism, wherein also ye are risen with him through the faith of the operation of God, who hath raised him from the dead.
(Col 2:13 KJV) And you, being dead in your sins and the uncircumcision of your flesh, hath he quickened together with him, HAVING FORGIVEN YOU ALL TRESPASSES;
So in the passage above we obviously see different information. Paul calls it "hidden wisdom." Paul says in 1 Corinthians 2:7 that "we speak the wisdom of God in a mystery." He says that it was hidden wisdom, that God ordained before the world unto our glory. In other words there was a MYSTERY pertaining to your salvation which was not made known until it was revealed to Paul, the apostle of the Gentiles.
Is it law:
(Mat 19:16 KJV) And, behold, one came and said unto him, Good Master, what good thing shall I do, that I may have eternal life?
(Mat 19:17 KJV) And he said unto him, Why callest thou me good? there is none good but one, that is, God: but if thou wilt enter into life, keep the commandments.
Or is it grace?
(Gal 5:4 KJV) Christ is become of no effect unto you, whosoever of you are justified by the law; ye are fallen from grace.
Ephesians 2:8 For by grace are ye saved through faith; and that not of yourselves: it is the gift of God:
(1 Cor 15:3 KJV) For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures;
(1 Cor 15:4 KJV) And that he was buried, and that he rose again the third day according to the scriptures.
In the book of Acts you don't see Peter preaching that do you? The reason being that Peter didn't know that. Peter preached the "baptism of repentance for the remission of sins" just as John the Baptist had earlier. The remission of sins looked forward to a future day of atonement for Israel at the second coming of Christ. The last recorded preaching of Peter is in Acts chapter ten.
What Peter said:
(Acts 10:34 KJV) Then Peter opened his mouth, and said, Of a truth I perceive that God is no respecter of persons:
(Acts 10:35 KJV) But in every nation he that feareth him, and worketh righteousness, is accepted with him.
What Paul said:
(Titus 3:4 KJV) But after that the kindness and love of God our Saviour toward man appeared,
(Titus 3:5 KJV) Not by works of righteousness which we have done, but according to his mercy he saved us, by the washing of regeneration, and renewing of the Holy Ghost;
Is salvation by grace or is it by works?
(Rom 11:6 KJV) And if by grace, then is it no more of works: otherwise grace is no more grace. But if it be of works, then is it no more grace: otherwise work is no more work.
There is no work, no religious activity involved today where your salvation is concerned. Jesus Christ did ALL the work and the work is finished. He suffered your punishment, he died your death. God made him to be sin for us that we might be made the righteousness of God IN HIM. So all that is necessary for salvation today is to put your trust in the risen Lord Jesus Christ. Believe on the Lord Jesus Christ and be saved.
Now, did something change?
2 Timothy 2: 15 Study to shew thyself approved unto God, a workman that needeth not to be ashamed, rightly dividing the word of truth.
You will find that Paul defines the "word of truth" as being the "gospel of YOUR salvation" in Ephesians 1:13. The gospel of YOUR salvation is not the gospel of the Kingdom committed to the 12 Apostles, which includes Peter. It is the salvation message committed to Paul, the Apostle of the Gentiles.