The Gospel is the good news that must be shared with the whole world. The Gospel is that God so loved the world that He gave His only begotten Son, that whosoever believeth on Him shall have everlasting life. The Gospel or good news is that Jesus Christ died on the cross at Calvary to pay the sin debt of the world. He took our place and paid for our sins, so that we could have eternal life. Then, Jesus resurrected on the third day. It is written in Romans 4.25: Who was delivered for our offences, and was raised again for our justification. By Jesus' death and resurrection, He conquered sin and death.
It is written in 1 Corinthians 15.1-28: Moreover, brethren, I declare unto you the gospel which I preached unto you, which also ye have received, and wherein ye stand; by which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain. For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures; and that he was buried, and that he rose again the third day according to scriptures; and that he was seen of Cephas, then of the twelve: After that, he was seen of above five hundred brethren at once; of whom the greater part remain unto this present, but some are fallen asleep. After that, he was seen of James; then of all the apostles. And last of all he was seen by me also, as of one born out of due time. For I am the least of the apostles, that am not meet to be called an apostle, because I persecuted the church of God. But by the grace of God I am what I am; and his grace was bestowed upon me was not in vain; but I labored more abundantly than they all; yet not I, but the grace of God which was with me. Therefore whether it were I or they, so we preach, and so ye believed. Now if Christ be preached that he rose from the dead, how say among you that there is no resurrection of the dead? But if there be no resurrection of the dead, then is Christ not risen; and if Christ be not risen, then is our preaching vain, and your faith is also vain. Yeah, and we are found false witnesses of God; because we have testified of God that he raised up Christ; whom he raised not up, if so be that the dead rise not. For if the dead rise not, then is not Christ raised; and if Christ be not raised, your faith is in vain; ye are yet in your sins. Then they also which are fallen asleep in Christ are perished. If in this life only we have hope in Christ, we are of all men most misterable. But now is Christ risen from the dead, and become the firstfruits of them that slept. for since man came death, by man came also the resurrection of the dead. For as in Adam all die, even so in Christ shall all be made alive. But every man in his own order: Christ the firstfruits; afterward they that are Christ's at his coming. Then cometh the end, when he shall have delivered up the kingdom of God, even the Father; when he shall have put down all rule and all authority and power. For he must reign til he hath put all enemies under his feet. The last enemy that shall be destroyed is death. For he hath put all things under his feet. But when he saith all things are put under him, it is manifest that he is excepted, which did put all things under him. And when all things shall be subdued unto him, then shall the Son also himself be subject unto him that put all things under him, that God may be all in all.