Christ's earthly ministry was to the lost sheep of the House of Israel. He and his Disciples/Apostles preached the "Kingdom Gospel." That message related to a future time when Christ will return to earth and reign on the throne of David over His people, Israel. Christ chose Paul to preach a separate Gospel (The Grace Gospel) to the Gentiles. Today, the Grace Gospel includes both Jew and Gentile alike. Today, there is no Kingdom Gospel, just the Grace Gospel. It is offered to anyone hearing the Gospel and placing all their faith in Christ alone for their salvation and eternal life, etc.
I don't think Paul preached a gospel different from the gospel that Christ preached.
Romans 15:19 Through mighty signs and wonders, by the power of the Spirit of God; so that from Jerusalem, and round about unto Illyricum,
I have fully preached the gospel of Christ.
2 Corinthians 10:14 For we stretch not ourselves beyond our measure, as though we reached not unto you: for we are come as far as to you also in preaching the gospel of Christ:
And Paul cautioned against the preaching of another gospel:
Galatians 1:7-8 . . . but there be some that trouble you, and would pervert the gospel of Christ. 8 But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed.
In the gospel that Christ preached, He called people to repent:
KJV Mark 1:14-15 14 Now after that John was put in prison, Jesus came into Galilee, preaching the gospel of the kingdom of God, 15 And saying, The time is fulfilled, and the kingdom of God is at hand:
repent ye, and believe the gospel.
The call to repent is the same call God issued in the OT:
NKJ Ezekiel 18:30 " Therefore I will judge you, O house of Israel, every one according to his ways," says the Lord GOD. "
Repent, and turn from all your transgressions, so that iniquity will not be your ruin.
And Paul preached that God now commands all people to repent:
NKJ Acts 17:30 "Truly, these times of ignorance God overlooked, but now commands all men everywhere to
repent