While I may be in school, I want to make sure that my exegetical skills don't erode too much. I'm going to try, when I can, to work my way through Paul's letters in chronological order in addition to working on papers for the Christian Way of Life project. The next couple of years the pace will probably be slow due to school, but hopefully by 2030 I can finish all of them. These won't be quite as thorough as some of my other studies have been and will cover larger chunks of text, at least while I'm in school. For 1 Thessalonians I will be using the commentaries of Gaventa, Malherbe, and Fee. No promises as to when the second section will appear.
You can read the text here.
Paul opens his letter by greeting the Thessalonians on behalf of his missionary team, and noting their spiritual location. They are under the influence of/in the sphere of God the Father and the Lord Jesus Christ. How thoroughly in the sphere of, there isn't enough to know right off the bat.
Paul then proceeds to his thanksgiving where he tries to show how much he cares despite the fact that he was only in Thessalonica for a short time. The Thessalonians excel by demonstrating their fidelity through their trusting, love filled, hopeful working out of their commitment to God. As Malherbe and Fee note, the 'For' at the start of verse 4 is not causal, but explains that what the Thessalonians have displayed proves that God has indeed chosen them, which should bring about further comfort. The proof of their election is really one fold, though it may appear to be two. It's the work of the Holy Spirit, who they experienced and brought them to a life of fidelity, both in belief and practice. So great was the work of the Spirit, that their faithfulness was joyful, even in the face of opposition and persecution, much like Paul's was. So great was the work of God in them.
As a result, all over Greece, people came to know about the work of God in them. Their lifestyle and allegiances were radically altered. No longer did they serve the gods of their world, but instead the one true God, who ruled through his Son, the crucified, raised, and exalted Messiah. A Messiah who will return one day to judge the evil oppressors of the Thessalonians and bring them final vindication and salvation.
As Malherbe notes, one unique feature of the early Christian movement, as evidenced in this letter, is the way religion and ethics were tied together. They were assumed to be different spheres. Wright, also explores this at length in Paul and the Faithfulness of God, noting that Christianity may be better understood in some ways as an ancient philosophy than an ancient religion. I think it certainly falls into both categories, then and now. The reason behind it all, is the Christian hope. If Jesus judges justly when he returns then the two are inseparable.
 The exact extent of the introductory thanksgiving is difficult to determine, but I think Fee is probably correct in only see verses 2 and 3 as comprising it.
 As Fee further notes, election is always reflecting a reality after the fact and as an expression of God's love and, with one exception, is corporate. Also, Fee makes the observation that salvation is positional, meaning an objective reality based on their position, "in Christ," or perhaps one could say based on membership in his people.
 Gaventa is particularly strong in bringing out how theocentric 1 Thessalonians 1 is.