If you read Ephesians 3, Paul was given lots of revelations from the ascended Christ Jesus, that no OT prophet, nor the 12 apostles, ever received. It was all hidden in God.
For this cause I Paul, the prisoner of Jesus Christ for you Gentiles,
2 If ye have heard of the dispensation of the grace of God which is given me to you-ward:
3 How that by revelation he made known unto me the mystery; (as I wrote afore in few words,
4 Whereby, when ye read, ye may understand my knowledge in the mystery of Christ)
5 Which in other ages was not made known unto the sons of men, as it is now revealed unto his holy apostles and prophets by the Spirit;
6 That the Gentiles should be fellowheirs, and of the same body, and partakers of his promise in Christ by the gospel:
7 Whereof I was made a minister, according to the gift of the grace of God given unto me by the effectual working of his power.
8 Unto me, who am less than the least of all saints, is this grace given, that I should preach among the Gentiles the unsearchable riches of Christ;
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: