1 Thessalonians: Structure

The first letter to the Thessalonians is not very rigidly constructed. The style is quite spontaneous and hardly polished.

Like most ancient letters 1 Thessalonians begins according to a fixed pattern by stating the sender, those to whom it is sent, a greeting and thanksgiving to God or the gods for the recipients. 1 Thessalonians 1:1 includes the senders, addressees and the greeting (“May grace and peace be yours”). 
The thanksgiving follows in 1 Thessalonians 1:2–3:13 and is as far as we know the longest Paul ever wrote. 
1 Thessalonians 4:1–5:24 contains the middle section, in which the three main subjects of the letter are dealt with. These subjects are separated clearly by the use of the word “about” (see 1 Thessalonians 4:9; 1 Thessalonians 4:13; 1 Thessalonians 5:1). The letter ends in 1 Thessalonians 5:25-28 with final greetings.