The Gospel

What is the good news of Jesus Christ?
Here is a brief summary:

God is the Creator of all things (Gen 1:1; John 1:3). He created man in his own image (Gen 1:27), and we are accountable to him as our Creator.

God is also holy and just (Isa 6:3; Gen 18:25). But we have sinned against him (Rom 3:23). The wages of our sin is death (Rom 6:23) and separation from God (Isa 59:2).

God is love (1 John 4:8). He sent his Son Jesus Christ (John 3:16) to become man (John 1:14). Christ humbled Himself, took on the form of a slave, and subjected himself to death, even death on the cross (Phil 2:6-11).

When Christ died on the cross, he bore the wrath of God that we deserve (Rom 3:25; Gal 3:13). While we were yet sinners, he died for us (Rom 5:8). Jesus was then buried in a tomb and rose again on the third day having defeated sin and death (1 Cor 15: 3-4, 54-55; 2 Tim 1:10) so that we might have life.

If we turn from our sins (Acts 3:19) and place our full trust and hope in Jesus (Acts 16:31) and what he did for us on the cross (Rom 10:9), God will forgive us our sins and put us in a right relationship with himself (Rom 5:10). We will be freed from our bondage to sin (Rom 6:18), and we will have eternal life with him in his glory (John 3:16; 17:3).

If, however, we do not turn from our sins and look to Christ for salvation, we will receive the just punishment we deserve for sinning against such a holy, loving God (John 3:36; Rev 20:15).

Turn from your sins. Put your full trust and hope in the one who bore God’s wrath for us. Call upon the name of the Lord for salvation (Rom 10:13). For salvation is only found in Christ (Act 4:12). 
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If you want to understand more about the Gospel, I would recommend you read through the Gospel of John which was written "that you might believe that Jesus is the Christ, the Son of God; and that by believing you might have life in His name" (John 20:31).
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For further explanations of the Gospel,  I recommend the following:
The Gospel of Jesus Christ
What is life all about?
There are only two ways to live.
The Gospel in Six Minutes (audio and text)
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For a short book that explains the Gospel, I recommend:
The Truth of the Cross by R. C. Sproul (eBook)
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And here are some audio sermons that explain what the Gospel is all about:
The Heart of the Gospel
Cristo Murió Por Nosotros (Español)