There is more than one gospel in the Bible.
The gospel God preached to Abraham.
Gal_3:8 And the scripture, foreseeing that God would justify the heathen through faith, preached before the gospel unto Abraham, saying, In thee shall all nations be blessed.
Gal_3:6 Even as Abraham believed God, and it was accounted to him for righteousness.
The gospel of the Kingdom.
Mat_4:23 And Jesus went about all Galilee, teaching in their synagogues, and preaching the gospel of the kingdom, and healing all manner of sickness and all manner of disease among the people.
The everlasting gospel.
Rev_14:6 And I saw another angel fly in the midst of heaven, having the everlasting gospel to preach unto them that dwell on the earth, and to every nation, and kindred, and tongue, and people,
Obviously we don't know the everlasting gospel because it is a future gospel.
And the gospel Paul preached.
1Co 15:3 For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures;
1Co 15:4 And that he was buried, and that he rose again the third day according to the scriptures:
Obviously all of the gospels are different.
God was dispensing his grace at different times to different peoples.
Abraham at that time was given the gospel " In thee shall all nations be blessed ".
Rom_4:16 Therefore it is of faith, that it might be by grace; to the end the promise might be sure to all the seed; not to that only which is of the law, but to that also which is of the faith of Abraham; who is the father of us all,
God was proclaiming the gospel to the Jewish Nation through Abraham.
Rom 15:8 Now I say that Jesus Christ was a minister of the circumcision for the truth of God, to confirm the promises made unto the fathers:
Israel was promised their kingdom of heaven would come to this earth.
Most of Israel did not accept Christ as their Messiah and her kingdom gospel that was preached by the Lord Jesus Christ.
The gospel Jesus preached is not our gospel.
We are not Israel.
We are not Gentiles.
Rom 15:9 And that the Gentiles might glorify God for his mercy; as it is written, For this cause I will confess to thee among the Gentiles, and sing unto thy name.
Rom 15:10 And again he saith, Rejoice, ye Gentiles, with his people.
Rom 15:11 And again, Praise the Lord, all ye Gentiles; and laud him, all ye people.
Rom 15:12 And again, Esaias saith, There shall be a root of Jesse, and he that shall rise to reign over the Gentiles; in him shall the Gentiles trust.
Anyone who is not saved is lost, Paul when he got saved was sent to the Heathens.
Gal 1:15 But when it pleased God, who separated me from my mother's womb, and called me by his grace,
Gal 1:16 To reveal his Son in me, that I might preach him among the heathen; immediately I conferred not with flesh and blood:
Paul was given the gospel by Christ to give to us.
Gal 1:11 But I certify you, brethren, that the gospel which was preached of me is not after man.
Gal 1:12 For I neither received it of man, neither was I taught it, but by the revelation of Jesus Christ.
This is the gospel you must believe to be saved.
1Co 15:3 For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures;
1Co 15:4 And that he was buried, and that he rose again the third day according to the scriptures: