The key to salvation is that we remember that salvation was accomplished for us on Calvary’s Cross by the Lord Jesus Christ, who, by His suffering and death, paid the penalty that we owe for the sins that we have committed. The devil wants mankind to want to reject that fact, and to take at least partial credit for our own salvation due to the good works that we have done.

Paul kept in touch with the Corinthians through the emissaries that he sent there, and had this back and forth, culminating in this second letter to the Corinthians that the Holy Spirit decided should become part of the canonical record.