I'll start with the question: "Do you think those two gospels are the same?"
See Luke 9:1-6 and see clearly: at that time they did not even know that Christ was to die. Read Luke 18:31-34. Note they did not have the slightest idea that Christ was to die. And yet, they were preaching the gospel of the kingdom and had been, for two years or longer.
Paul specifically states that the gospel of the grace of God is the preaching of the cross (1 Cor. 1:18), that Christ died FOR OUR SINS, was buried and rose again. That is the gospel of the grace of God. That by trusting in that finished work of Christ, we are saved by grace through faith in that finished work.
So, if the gospel of the grace of God is all about the preaching of the cross, and Peter and the 11 preached a gospel that obviously did not preach about the cross (they had no idea He what He was talking about when He predicted His death), how can they be the same gospel? They cannot.
The gospel which they preached was the "gospel of the kingdom" (Matt. 9:35, Luke 9:2), not the "preaching of the cross"(1 Cor. 1:18).
Here is another illustration> Luke 9:6 says that the apostles "departed, and went through the towns, PREACHING THE GOSPEL". It is assumed that they went forth preaching salvation through the cross, the gospel of the grace of God. Yet Luke 18:31-34 makes it clear that they had NO IDEA Christ would even die. Luke 9 makes this seeming contradiction all plain, for in verse 2 we read "And He sent them to preach THE KINGDOM OF GOD", NOT His death for sin.
Can you see the difference?
Jeus Christ said, “My kingdom is not of this world”. That’s the gospel; the hope of life everlasting. And he would be the key that opens the door, just as he told Nicodemas: “For God sent not his Son into the world to condemn the world; but that the world through him might be saved.” John 3:17
But he had to shed his blood to tear down the wall of sin that separated God from mankind. The testament was of no effect while the testator lived. It required the death of the testator, Jesus Christ.
Jesus Christ told Peter, in Luke 22:32, that “When thou art converted strengthen the brethern”. He told them to tarry in Jerusalem for the promise of the Father.
**Paul specifically states that the gospel of the grace of God is the preaching of the cross (1 Cor. 1:18), that Christ died FOR OUR SINS, was buried and rose again. That is the gospel of the grace of God.**
So, you don’t think that that was same message Peter preached to Cornelius and his household? His message began this way: “Of a truth I perceive that God is not respecter of persons: But in EVERY nation he that feareth him, and WORKETH righteousness, is accepted with him”.(Acts 10:34,35).
Just as he did to the Jews (in Acts 2:14-36), He preached to Cornelius, Christ and him crucified, the resurrection, and remission of sins to those that believe. Acts 10:36-43. Verses 44-48 show their conversion.
In Acts 19, Paul preached Jesus Christ to the Ephesians. Verses 1 and 2 show that these were believers, for Paul asked them if they had “received the Holy Ghost since ye believed”. If you notice, the next two verses (3 and 4) show NO teaching of Christ’s death, buriel, and resurrection. That’s because they already believed it. It was THEN (vs 5) that “they were baptized in the name of the Lord Jesus”.
Then Paul laid hands on them, and they received the Holy Ghost. (vrs 6)