The Gospel message is simple. Place your faith in Jesus Christ.
This is love: not that we loved God, but that he loved us and sent his Son as an atoning sacrifice for our sins. 1 John 4:10 (NIV)
If you’re interested in learning more about Christianity and why we believe what we believe, you might want to check out one of these books:
The book of John or one of the other Gospels (Matthew, Mark, Luke) in the New Testament portion of the Bible