First Corinthians 15:1-2 is one of the reasons why I am convinced that the gospel is not just for non-Christians. Whether you are only two months in the faith or over twenty years, you need to hear the gospel – the life, death and resurrection of Jesus for us – over and over and over again.
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. (1 Corinthians 15:1-2 ESV)
The gospel, therefore, must be central to everything in your life, everyday of your life.
For those united to Christ the truth of the gospel always produces a tranformed life, which can be sustained in an ongoing way only by the power of the gospel. Thus the gospel is not only something we embrace at the beginning of the Christian life (“which you received”), but the source of strength throughout the Christian life (“in which you stand”). It is remarkable that Paul sees a need to remind the Corinthians – already believers! – of the gospel. Evidently, the gospel message is not only for evangelism but also for discipleship; not only for unbelievers, but also for believers. (ESV Gospel Transformation Bible)
The gospel changes everything, absolutely everything. And that’s not an overstatement.