This commentary was one of the most highly regarded expositions of 1 and 2 Thessalonians in the latter half of the 20th century. Ernest Best points out that the Thessalonians have experienced some rough times, and that Paul is praising them for holding on to their faith and sharing it with others. He stresses that they they should keep this up, because the Lord is coming soon.
Best believes that Paul was responsible for both 1 and 2 Thessalonians and that the end times positions of the two epistles are not as different as critical scholars have suggested.
The commentary itself has the footnotes buried within the text of the commentary, which makes for tougher and choppier reading. Moreover, not everyone will be convinced that Best's interpretations are always best. For example, some will disagree with interpreting skenos in 1 Thessalonians 4:3 as a reference to the believer's "wife" rather than to the believer's own body.
Moreover, some will feel Best is chastising Paul too hard for his statement about the reference to the Jews killing Jesus in 1 Thessalonians 2:14. Best sees it as an example of Paul spouting anti-semitic rhetoric. But since Paul is Jewish and he elsewhere expresses his great love for his people (Romans 9-11), it would be better to see this as a bitter disagreement among family members. Paul is upset that many of his Jewish brothers have not only rejected the idea of Jesus' messiahship, but try to hinder others from coming to Christ. He castigates his Jewish brothers for their role in the death of Christ, just as the prophets of the Old Testament often castigated their own people for their role in rejecting God's will (Isaiah 1:4, 5:24, Jeremiah 2:11.
Best also discusses the teaching in 1 Thessalonians 4:13-18, rightfully noting that the final destination of the living and deceased believers in Christ is left "hanging in the air."
In 2 Thessalonians, he points out that Paul is not denying the suddenness of the Lord's return, but that he is qualifying it by teaching that it will come suddenly after the revelation of the man of lawlessness. This interpretation can be questioned.
Another questionable call is that Best sees the katechon holding back the man of lawlessness (2 Thess 2:6-7) as a reference to an evil person or force. But why would evil hold back evil? It's possible, but it makes better sense to say that good holds back evil.
It's not always easy to read, but you will learn a lot from this commentary. Read it along with Leon Morris' Eerdmans commentary on these epistles.