The Gospel is the good news
of the death and resurrection of Jesus Christ, the incarnate Son of God and Mediator of the covenant of grace, who justifies, sanctifies, and adopts His people through faith alone to the hope of eternal life with God in the physical new creation.
The good news is:
biblical (Jesus' death and resurrection are according to the Scriptures),
theological and salvific (Jesus died for our sins, to reconcile us to God),
historical (if the saving events did not actually happen, our faith is worthless),
apostolic (the message was entrusted to and transmitted by the apostles, who were witnesses of these saving events), and personal.