Paul finds himself trying to ward off the attacks of the Judaizers who are following him. In order to counter their claims that he is a greedy manipulator, he proclaims that the Thessalonians themselves are his apologia – evidence that he is a messenger of God with the message of God. Their transformed lives provide the apologetic for him. The life and the gospel that he invested in their lives has born fruit!
John Maxwell says, “You teach what you know; You reproduce what you are.” That’s the nature of the lectionary texts this week.
There are other angles that you can take as well. The structure of I Thess 2:1-8 is linked to 1 Thess 1:5-6, and it may be that 2:1-8 is an exposition of 1:5-6. It could be that Paul, in his encouragement to the people is also encouraging himself. He is being reminded of the transformation that is occurring.
We need to be taken back sometimes to points in time when God showed up. The Old Testament people would build altars as a reminder. Maybe we need to follow their lead so that we can plow through periods of doubt.