Paul was writing to a mixed congregation.  We know that some of the Jews were converted, as well as numerous Gentiles.  But Paul does not cover in depth any of the great themes of the Christian revelation.  Rather he refers to their faithful acceptance of the gospel and their steadfastness under persecution 1 Th 2:13-14).  The instruction he gives them is about how to live in a way pleasing to God:  "be sanctified" (1 Th 4:3), avoid sexual immorality, love the brotherhood, "mind your own business" and work hard. 

He spends more time writing about the last days -- the return of Christ:  Jesus will come from heaven, the dead in Christ will be raised up, and then the living.  Believers should live in faith and expectation, and not be caught napping and unprepared like unbelievers (1 Th 5:1-11).

The second letter continues the subject of Christ's return.  This time he teaches about the "man of lawlessness" who will precede the return of Christ, and exalt himself against God.  Jesus will destroy this enemy upon his return.  All of this is a reminder of what he told them in person (2 Th 2:5).   So we are missing the core teaching that he had given them earlier.  There is no reference in these letters to any Old Testament Scriptures, patriarchs or prophets, or laws.  Paul encourages them to stand firm in the teaching they have received, and again -- to work hard.  "Follow our example" (2 Th 3:7).