What is the Gospel?
The Gospel is good news . . . about Jesus Christ.
Simply put, the gospel is good news. It is the news that Jesus Christ died on the cross for the sins of the world, was buried in a tomb, and rose from the dead three days after his death. Paul wrote to the believers in the city of Corinth:
Now I would remind you, brothers, of the gospel I preached to you...that Christ died for our sins in accordance with the Scriptures, that he was buried, that he was raised on the third day in accordance with the Scriptures. (1 Corinthians 15:1, 3-4)
That is the content of the gospel - the gospel facts; and Scripture tells us how to appropriate those facts so they impact our lives for eternity:
Acknowlege Your Sin: The good news of the gospel loses its impact without first confronting the bad news. Scripture tells us that we are all born in sin. We have no spiritual life because we are in bondage to sin and we are therefore in danger of God's judgment. The book of Romans says that the wages of sin is death - eternal death without Christ in Hell. Here's how it describes our condition:
None is righteous, no, not one; no one understands; no one seeks for God. All have turned aside; together they have become worthless; no one does good, not even one. (Romans 3:10-12)
In order to be reconciled to God you must acknowledge your need of forgiveness.
Turn From Your Sin: Once you have acknowledged that you are in desperate need of a remedy for your sinful state, Scripture calls you to repent. Acts 17:30 says:
[God] commands all people everywhere to repent, because he has fixed a day on which he will judge the world in righteousness.
It is not enough for you to simply feel sorry for your sins. You must turn from them. Doing so reveals that you have understood your grave situation and God has made you willing to abandon your sinful ways.
Believe In The Savior: Believing in Jesus Christ means that you trust him alone for your eternal salvation. Believing is the second half of repenting. Jesus told the crowds in Galilee to:
...repent and believe in the gospel. (Mark 1:15)
These two words are the most concise way to explain the truth of the gospel: repent and believe. You repent of your sins and believe in Jesus Christ. This is where you appropriate the gospel facts. You must trust Christ to save you from your sins because you believe and accept that he died, was buried, and rose again.
Follow The Savior: The proof that God has indeed transformed your life through the gospel is that you follow Christ. Belief that simply claims to accept the gospel facts but does not produce a transformed life is not truly belief. Paul wrote:
Therefore, if anyone is in Christ, he is a new creation. The old has passed away; behold, the new has come. (2 Corinthians 5:17)