"For God so loved the world, that he gave his only Son, that whoever believes in him should not perish but have eternal life."
John 3:16 ESV
The Gospel literally means good news. What is the good news that we believe? The good news for everyone is that the one true God who is just and gracious has looked at us, sinners. And although He could have judged us for our sins, He has instead sent his perfect Son, Jesus Christ, who is fully man and fully God, to die on the cross in our place for our sins. Jesus Christ bore the full wrath of God and in His death and in His resurrection, Christ was victorious over sin and death. Therefore, anyone who believes in this and turns from their sin and trusts in Jesus Christ as the true Savior and Lord will be reconciled to God for eternity.