The gospel is the good news about the work Jesus Christ has done to reconcile sinners to God.
There is only one true God. He is holy and He made mankind in His image (Gen 1:26-28).
The first man and woman, Adam and Eve, lived in perfect harmony with God, with each other, and with all of creation. God gave them free reign over all of creation and told them to eat of any plant they wanted to, but they must not eat of this one tree. (Gen. 2: 16-17). But Adam and Eve chose to disobey and they sinned against God. Their sin cut them off from God (Gen. 3). Since then mankind has been tainted with sin (Rom. 3:23).
But God, in his amazing love, sent His son, Jesus, to the earth to rescue His people (Rom. 5:8, Luke 1:67-79). Jesus lived a perfect life, free from sin, and died the death all mankind should have died. By dieing on the cross Jesus took on the sins of many (Mark 10:45, Rom 3:21-26). Following his death Jesus was buried, but on the third day he rose from the grave, defeating death. God's wrath against sin has been poured out on Jesus Christ for those who believe.
He calls us all to repent from our sins and trust in the work of Jesus to bring us back to God (Rom. 8:1-3). When we do that we are born into a new life, putting to death the old self and living forever in Him and with Him (John 3:3, 16-18; Luke 9:23; Galatians 5:24; 1 Peter 2:24).
One day God will judge all mankind. Only those who are saved by grace through faith in Jesus Christ will live forever. God must and will punish sin (Rom. 2:5-8). Then God will restore creation and bring about a new heaven and a new earth. All who are in Jesus Christ will live with Him and enjoy Him forever (Rev. 21:1-8)!