The gospel is the “good news” because it contains the exceedingly wonderful message of God’s redemption of sinful humanity through the death, burial, and resurrection of His Son, Jesus Christ. 

The good news of the gospel is that God offers salvation to humanity through the death, of His Son, The Lord Jesus Christ, providing forgiveness for sins. 

The gospel is the message about salvation, It is the message that Jesus, being God in the flesh, took the penalty for human sin upon Himself, died for the sin of humanity and rising again the third day according to the Scriptures. 
1 Corinthians 15:3,4

Sin has separated us from God (Romans 3:23)
But when Jesus died on the cross, He paid the price and canceled the debt of sin for all who would believe in Him. (Isaiah 53:5) (Colossians 1:20) 
The Lord Jesus Christ was crucified and died as a sufficient sacrifice for all of the human race, and is the only Mediator between God and man, was physically raised from the dead and is in Heaven, anyone who accepts Jesus Christ as Lord and Saviour by faith alone, is born into the family of God, receives the gift of eternal life, and enjoys the forgiveness of their sins. 
(John 1:12, John 3:16, John 10:28, 1 John 2:12, 1 Timothy 2:5,6)

The gospel is good news because, through personal  faith and trust in
The Lord Jesus Christ, there is assurance of eternal life and peace with the Saviour. (Romans 6:23, Romans 10:17)