The letter concludes in Paul's typical way -- with a request some admonitions and encouragement. He asks for prayer for his work -- that the gospel would spread rapidly and for protection. His admonition in this letter is about idleness and idlers. The Biblical principle is for everyone to work and provide for themselves. Obviously, there are exceptions, Biblically, for widows and others unable to care for themselves. But the general rule is to not live on the generosity and charity of others but for each to "pull their own weight". Verse 10: anyone not willing to work should not eat. He then warns against those idlers to are just being busybodies and stirring up trouble for others.
Verse 13 serves as a grace note and a warning to me. Paul says "Brothers and sisters do not be weary in doing what is right." This passage often puzzled me until I realized that it was quite possible to become exhausted and weary from "doing the Lord's work". It is also possible to get fatigued from always being on the other side of the majority (standing for the oppressed, the disadvantaged, the down and out). And yet, we are not to weary in doing what is right. This has two possibilities for me: 1) that I should just persevere on and not give up no matter how difficult the battle becomes. This is good encouragement and good advise. Option 2) is a reminder to seek balance in life. It is important for all of us to withdraw, to rest, to reflect, to keep a sabbath, and to not be overwhelmed with the work of ministry.