The Gospel is the good news that through Jesus Christ, we can be saved from sin and eternal separation from God. The Bible teaches that all have sinned and fall short of the glory of God (Romans 3:23). Because of sin, we are deserving of eternal punishment (Romans 6:23), but God, in His love and mercy, provided a way of salvation.
Jesus Christ, the Son of God, was sent to die for our sins. He lived a perfect life and was crucified on the cross, shedding His blood to pay the penalty for our sin (John 3:16, 1 Peter 2:24). Jesus rose from the dead on the third day, proving that He has power over sin and death (1 Corinthians 15:3-4).
Salvation is by grace through faith, not by our works or good deeds. The Bible clearly states that we are saved by grace through faith in Christ, and not of ourselves, it is the gift of God (Ephesians 2:8-9). To receive salvation, we must repent of our sins and believe on the Lord Jesus Christ (Acts 16:31, Romans 10:9).
When we repent and trust Christ, we are born again (John 3:3), and God promises eternal life to all who believe (John 3:36). This is the Gospel: the gift of salvation freely offered to all who will receive it through faith in Jesus Christ.