Notice the mention of Timothy. Acts chapter 16 mentions how Paul found him and he became part of the team. He is left here at Thessalonica to establish and encourage them concerning their faith.
Paul in these verses tells them they were not to be shaken by the persecution they were going through. Paul was concerned not hearing about them for a time. He mentions something interesting here about the old devil, called the tempter. He is always seeking to deter Christians from their faith. I have seen this many times in many places. In one place Paul says, “We are not ignorant of his devices.” I am afraid people are sometimes.