The word "gospel" simply means good news. In the Bible the word gospel is used primarily in two ways. First we have Jesus Christ preaching the gospel of the kingdom in the synagogues, offering the kingdom to the Jews. John the Baptist came preaching to them to prepare for their King. Jesus preached and taught about the coming kingdom, Matthew 4:17, and the disciples also preached the gospel of the coming kingdom, Matthew 10:7.
Jesus came only to the Jews and throughout the first four books of the New Testament and we find Jesus preaching the gospel of the kingdom, which is the coming millennial kingdom over which Jesus will be King, Matthew 4:23; 9:35; 24:14. Jesus appointed the apostle Paul to preach to the Jews and Gentiles the gospel of grace or salvation, 1 Corinthians 15:1-4.
Most Christians, when talking about the gospel, are referring to the gospel of the grace of God given to the apostle Paul. This is about the death burial and resurrection of Christ and what it accomplished, 1 Corinthians 15:1-4. Later Paul gives more details, 1 Corinthians 15:12-45. These passages take us back to the book of Genesis.
In 1 Corinthians 15:21 and Romans 5:12 we find that by one man sin entered and death by sin so that death passed upon all men. This refers to Adam and his sin in Genesis 3:17-19.
Then in 1 Corinthians 15:22 it says that even so in Christ shall all be made alive. In Romans 6:23 we find that sin earns wages and the wages are death. This death is that of the second death, Revelation 21:8, which is an eternal separation from God in a lake of fire and is a death we cannot pay and go to heaven. So Christ came to earth to give His life in our place and when we accept what He did on the cross for us by faith, we have His righteousness imputed to us, Romans 4:20-24. After explaining the bad news of death by sin, Paul then tells us of the good news of salvation in Christ, Colossians 1:13-17.
To pay for our sin we need a perfect man to die for sin. Jesus Christ is this perfect man who never committed one sin, who was made to be sin for us, 2 Corinthians 5:21; 1 Peter 2:22; 1 John 3:5. The only solution was for Christ to come to the earth, become a man so He could be our Savior. Paul continues on in Corinthians to tell us about the final victory that overcomes the effects of the fall of Adam, 1 Corinthians 15:46-57.
There is a problem around this plan of the world receiving the gospel of salvation. Paul says that Satan blinds the mind of those that don't believe, in order to keep the gospel of Christ hidden, 2 Corinthians 4:3-4. Jesus, explaining the seed that fell by the way side, Matthew 13:4, said when one heard the Word and did not understand it, the devil snatches the Word away, Matthew 13:38-39. Then again, Jesus explains about the person who receives the Word in stony places, Matthew 13:5, the seed has no root and falls away when faced with trouble for expressing interest in the Word, Matthew 13:57; 15:12. Another example that Jesus addresses is the seed that was sown among the thorns in Matthew 13:7. Jesus explains in Matthew 13:22 that the cares of this world and the deceitfulness of riches choke out the Word. Then Satan also has counterfeit Christians, 2 Corinthians 11:26, and these believe a counterfeit gospel, Galatians 1:6-9.
Paul said in Romans that whosoever shall call upon the name of the Lord shall be saved. How shall they call on Him without someone being sent to give them the gospel of peace, Romans 10:13-15. As Christians we should never be ashamed of the gospel nor be slow to share it. The gospel is the power of God unto salvation to everyone who believes. The righteousness of God is revealed in the gospel, Romans 1:16-17. Paul said that faith comes by hearing and hearing by the Word of God, Romans 10:17. The Word comes in power and in the Holy Spirit and with assurance, 1 Thessalonians 1:5.
When we first exercise faith in Christ we are justified. It is called justification and is a declaration of our righteousness. It is the righteousness of Christ imputed to us, transferred to us, at the moment we trust Christ, Philippians 3:9. Our unrighteousness is exchanged for the righteousness of Christ at the moment we trust Christ. Imputation and justification are instantaneous at the moment of trusting Christ. Next comes sanctification. Sanctification is a process of the believer's life gradually becoming more and more like Christ, as we grow in the understanding of the Word. This is a process that will continue until our dying day or the rapture of the church, whichever comes first. Then after the rapture there is the glorification that takes place and we are freed from our potential to sin and ushered into the presence of God, 2 Corinthians 5:8; Philippians 1:21-23. Justification frees us from the penalty of sin, Sanctification frees us from the power of sin, and glorification frees us from the presence of sin.