B
When we examined Matthew 16:21-22, Luke 18:33-34, and John 20:9 we see that during Christ's earthly ministry, the twelve apostles did not know that Jesus Christ was going to die and rise again from the dead. Even though Christ had told them this plainly on several occasions, it was hidden from them by God. Paul received the gospel of grace by direct revelation from the Lord Jesus Christ. He was appointed as the apostle of the Gentiles to reveal mysteries previously kept hidden. One of these is the mystery of the gospel. Paul writes in Ephesians 6:18-20 "Praying always ... for me, that utterance may be given unto me, that I may open my mouth boldly, to make known the mystery of the gospel for which I am an ambassador in bonds ...." Paul's gospel had been a mystery, not been known to anyone before God revealed it to him.
Keep in mind that Ephesians was written around 62 AD, about 30 years after Jesus Christ had ascended into heaven. Paul had already completed his first three missionary journeys. Now let's look at Ephesians chapter 3, beginning with verses 1-4. "For this cause I Paul, the prisoner of Jesus Christ for you Gentiles, If ye have heard of the dispensation of the grace of God which is given me to you-ward: How that by revelation he made known unto me the mystery: (as I wrote afore in few words Whereby, when ye read, ye may understand my knowledge in the mystery of Christ) ...." So we see that God by "revelation" showed Paul the "mystery" which no one knew before. This is why Paul calls it "my knowledge". "Which in other ages was not made known unto the sons of men, as it is now revealed unto his holy apostles and the prophets by the Spirit ..." (Ephesians 3:5). Note the change in tense here. Compare "is now revealed" (to the apostles around 62 AD) with "he made known unto me" (Paul) by revelation at some earlier time. Then in Ephesians 3:9, "And to make all men see what is the fellowship of the mystery, which from the beginning of the world hath been hid in God, who created all things by Jesus Christ ...."
In about 66 AD, Peter, near his death, acknowledged that God had revealed many mysteries to Paul. He writes in 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(not "unto us", but "unto him") hath written unto you; As also in all his epistles, speaking in them of these things hard to be understood ...." Peter was writing this epistle to Jews, so the epistle of Paul that Peter was referring to was Hebrews. From Romans 16:25, it is evident that the what Paul calls "my gospel", was a mystery until God showed it to him by revelation. "Now to him that is of power to stablish you according to my gospel, and the preaching of Jesus Christ, according to the revelation of the mystery, which was kept secret since the world began ...."
Why did God keep our gospel a secret for so long? "But we speak the wisdom of God in a mystery, even the hidden wisdom, which God ordained before the world unto our glory: Which none of the princes of this world knew: for had they known it, they would not have crucified the Lord of glory" (1 Corinthians 2:7-8). So no one was allowed to know it, not Peter, the apostles, Judas, Pilate, the demons, or even Satan himself.
Keep in mind that Ephesians was written around 62 AD, about 30 years after Jesus Christ had ascended into heaven. Paul had already completed his first three missionary journeys. Now let's look at Ephesians chapter 3, beginning with verses 1-4. "For this cause I Paul, the prisoner of Jesus Christ for you Gentiles, If ye have heard of the dispensation of the grace of God which is given me to you-ward: How that by revelation he made known unto me the mystery: (as I wrote afore in few words Whereby, when ye read, ye may understand my knowledge in the mystery of Christ) ...." So we see that God by "revelation" showed Paul the "mystery" which no one knew before. This is why Paul calls it "my knowledge". "Which in other ages was not made known unto the sons of men, as it is now revealed unto his holy apostles and the prophets by the Spirit ..." (Ephesians 3:5). Note the change in tense here. Compare "is now revealed" (to the apostles around 62 AD) with "he made known unto me" (Paul) by revelation at some earlier time. Then in Ephesians 3:9, "And to make all men see what is the fellowship of the mystery, which from the beginning of the world hath been hid in God, who created all things by Jesus Christ ...."
In about 66 AD, Peter, near his death, acknowledged that God had revealed many mysteries to Paul. He writes in 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(not "unto us", but "unto him") hath written unto you; As also in all his epistles, speaking in them of these things hard to be understood ...." Peter was writing this epistle to Jews, so the epistle of Paul that Peter was referring to was Hebrews. From Romans 16:25, it is evident that the what Paul calls "my gospel", was a mystery until God showed it to him by revelation. "Now to him that is of power to stablish you according to my gospel, and the preaching of Jesus Christ, according to the revelation of the mystery, which was kept secret since the world began ...."
Why did God keep our gospel a secret for so long? "But we speak the wisdom of God in a mystery, even the hidden wisdom, which God ordained before the world unto our glory: Which none of the princes of this world knew: for had they known it, they would not have crucified the Lord of glory" (1 Corinthians 2:7-8). So no one was allowed to know it, not Peter, the apostles, Judas, Pilate, the demons, or even Satan himself.