The 12: Proclaimed the long-awaited Kingdom as at hand (Matt 10:6) and with it times of refreshing and restoration of all things (Acts 3:19-21). All this God had revealed though various Old Testament prophets.
Paul: Proclaimed the secret of the Body -- the Church -- a plan God had kept hidden since the world began (see Rom 16:25; 1 Cor 2:7; Eph 1:4-11; 1:19-23; 3:5-9; Col 1:18).
Did you read--
Eph 3:1 For this cause I Paul, the prisoner of Jesus Christ for you Gentiles,
Eph 3:2 If ye have heard of the dispensation of the grace of God which is given me to you-ward:
Eph 3:3 How that by revelation he made known unto me the mystery; (as I wrote afore in few words,
Eph 3:4 Whereby, when ye read, ye may understand my knowledge in the mystery of Christ)
Eph 3:5 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;
Eph 3:6 That the Gentiles should be fellowheirs, and of the same body, and partakers of his promise in Christ by the gospel: