In the next two verses we are told to beware and avoid people who teach wrong doctrine. Paul names two men who taught wrong things about the resurrection. There are many doctrines. They are like cancer to the body of Christ, which is the church. The seal and foundation is that the Lord knows them that are His. We can’t always tell, but He knows. The rest of the chapter will say more.
The last phrase is that everyone who names the name of Christ should depart from iniquity. A so called Christian who can’t keep from a sinful life has lost his or her testimony and is useless as a servant of Christ. I don’t want to be that kind of person. Keep a good testimony as a Christian.