First and foremost, we must be clear about the Christian gospel. The Christian gospel is the good news that even though all are born sinners, eternal life is offered through Christ.
In a previous post, we stressed the importance of growing in grace. We don't have to go forward in the Christian life strictly through our own power. So this is a good place to review why God would work in our lives at all. Asked directly, "What is the gospel?"
The word "gospel" means "good news" and the good news is that even though we are all born in rebellion against God - - and continue to rebel apart from Christ - - God sent his only Son to die on the cross so that all who believe in Him might have everlasting life (John 3:16).
The Apostle Paul explicitly reviews the good news in 1 Corinthians 15:1-4:
Now I would remind you, brothers, of the gospel I preached to you, which you received, in which you stand, and by which you are being saved, if you hold fast to the word I preached to you—unless you believed in vain. For I delivered to you as of first importance what I also received: that Christ died for our sins in accordance with the Scriptures, that he was buried, that he was raised on the third day in accordance with the Scriptures, (1 Corinthians 15:1-4 ESV
For more, see Chris Brauns's post - What do Christians Mean When They Reference the Gospel or Good News? or take 3 minutes and 50 seconds to watch Ravi Zacharias review the gospel below.