5For this reason, when I could bear it no longer, I sent to learn about your faith, for fear that somehow the tempter had tempted you and our labor would be in vain.
The tempter is another name for Satan or the devil. Though the New Testament often speaks of Satan tempting or inciting people to do evil, it is only here and in Matthew 4:3 that he is actually called the tempter.
5 For this reason, when I could bear it no longer, I sent to learn about your faith, for fear that somehow the tempter had tempted you and our labor would be in vain.