From J.D. Greear’s book Gospel: Recovering the Power that Made Christianity Revolutionary
Nonbelievers need to hear the gospel to believe it and be saved. Believers need to be reminded of the gospel so they can grow deeper in Christ. There is really no distinction, you see, between what believers need to hear and what unbelievers need to hear. Both believers and unbelievers need to get a glimpse of God’s majestic glory, a taste of His surpassing beauty, and a sense of how much grace God has shown toward them in Christ. Both believers and unbelievers need to be rebuked for their pride and self-sufficiency, to be reminded of the all-surpassing beauty of God. They both need to be stirred up to faith. The gospel is the center of the message no matter who you are talking to. It is everything. Christ is all.