Eighteen months of daily interaction, not to mention others that were sent, additional visits, and a previous letter—and yet Paul still needed to write one of his longest epistles to the brethren at Corinth to deal with their spiritual struggles and immaturity.
Paul reminded them in the first chapter that he had been sent by Christ to preach the gospel to them (1 Cor. 1:17). He admits that when he came to Corinth he did so “in weakness and in fear and in much trembling” (1 Cor. 2:3). Luke confirms that fact in his account of Paul’s arrival in Corinth (Acts 18:9-10). However, without regard to Paul’s doubts and fears, he was sent by Christ and he was sent to preach the gospel to them and that is what he did.
The frequency with which he mentions the gospel (a dozen times) is itself an indication of how important the gospel was to Paul. More to the point, it also shows how important it should have been to them. That it wasn’t is evidenced by all the issues that Paul had to address in his letter.
The last major section of teaching in his letter was itself a treatise on the gospel.
Now I make known to you, brethren, the gospel which I preached to you, which also you received, in which also you stand, by which also you are saved, if you hold fast the word which 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 according to the Scriptures, and that He was buried, and that He was raised on the third day according to the Scriptures. 1 Corinthians 15:1-4
The entire 15th chapter deals with the gospel. In fact, that chapter in itself is a sermon to all Christians and ought to be reviewed on a frequent basis. In laying the foundation for what would follow, Paul stated five things in those first four verses.
I preached to you the gospel (15:1). Their self-absorption in things like preacher personalities (Chapter 1), walking in the flesh (Chapters 2 and 3), discrediting Paul (numerous references, Chapter 9), boasting in immorality (Chapters 4 and 5), taking one another to court (Chapter 6), making issues of marriage (Chapter 7), creating stumbling blocks by eating meat sacrificed to idols (Chapter 8), grumbling and being disobedient (Chapter 10), misunderstanding the purpose and value of worship (Chapter 11), the Lord’s Supper (Chapter 11), spiritual gifts (Chapters 12-14), and lacking in love for one another (Chapter 13) were not the result of the gospel that Paul preached. That behavior was the result of not abiding in it. The problem, manifested in all the above ways, was a lack of commitment to the gospel.
You also received the gospel (15:1). They were not Christians by birthright. They individually heard and then received (obeyed) the gospel. In other words, they started their Christian walk being set free from sins by receiving the gospel. They were again embroiled in sin by ignoring it.
You also stand in the gospel (15:1). The statement is only true if they remain true to the gospel. It is not saying that regardless of their problems, they are still in harmony and fellowship with God. Rather, the point is that the only way anyone can stand before God in their daily walk is if they stand in the gospel.
You also are saved by the gospel (15:2). As with the previous point, it assumes they are holding fast to the gospel. If they abandon it, they will lose their salvation.
The gospel is the truth about the death and resurrection of Jesus (15:3-4). That is the core message! Their salvation and our salvation depend upon remembering daily what Christ did for us and that God raised Him up. If we reflected more on this core truth, we would have fewer problems with sin. Are you receiving, standing, and saved?