What is the Gospel?
The gospel is simply the "good news" of Jesus Christ. The Scriptures explain that all of mankind has a serious problem, and it is that we are sinners against God and fall short of the glory of God (Romans 3:23). You see, the purpose of all of creation is to glorify God, and man as God's chief creation is to worship and enjoy Him forever (Revelation 4:11). We exist to magnify and glorify God, but our sin, which is a violation of God's law (e.g. lying, hatred, stealing, immoral thoughts, etc.), separates us from God who is holy and just (I John 3:4, Isaiah 59:2).
Since we are born sinners (Psalm 52:5), we stand condemned already in our guilt and spiritual deadness (John 3:18). Yet in God's perfect holiness––and this is the good news––God has, in His good pleasure, made a way for sinners to be reconciled to Himself through His Son Jesus Christ (I Corinthians 5:14-21, John 3:16-17). Jesus Christ, God's Son came to earth, was born of a virgin, died on the cross, and rose again three days later from the grave, breaking the power of sin and death. While on the cross, Jesus stood condemned before a righteous and holy God and absorbed the wrath of God that was due us. He absorbed the penalty of God's full wrath and died for the sins of His people.
The whole world is commanded to repent of their sin and to believe the Biblical gospel (Acts 3:19, Luke 24:47, Acts 17:30, Ezekiel 18:30-32, Matthew 3:2, Acts 20:21). The gospel, to them that believe, is the power of God unto salvation (Romans 1:16, I Corinthians 1:18).
God created and owns everything, including you (Genesis 1:1, Psalm 24:1). God is perfectly holy (Matthew 5:48). God requires your perfect obedience to His law (James 2:10). You have broken God’s law (Romans 3:10; 23). You will pay the eternal penalty for your sin (Romans 6:23). You cannot save yourself by your good works (Titus 3:5). Christ came to earth as both God and sinless man (Colossians 2:9). Christ demonstrated His love by dying on the cross to pay sin’s penalty (Romans 5:8; II Corinthians 5:21). Christ rose from the grave and is alive today (I Corinthians 15:4). You must repent of all that dishonors God (Isaiah 55:7; Luke 9:23). You must believe in Christ as Lord and Savior, and be willing to follow after Him (Romans 10:9).