What is the gospel?

Jesus: “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.

Kalle: The gospel is the good news that Jesus died in substitution for the sins of mankind and that as a result everyone who believes in the gospel can have eternal life through Jesus and must not die eternal death (the second death after the resurrection, see Rev 20; Rev 21) as a consequence of his sins.