Paul tells the Thessalonians to:
Paul’s prayer for the Thessalonians is that they will be sanctified (v. 23; see also 1 Thess 4:3) and that they will be ready for the return of the Lord. When the guidelines he gives in verses 16–22 are present in their lives, the Thessalonians show their progress toward being ready.
The Lord is coming back, and he is faithful. He will prepare us for his return. When we recognize evidence of his preparation, we should rejoice and remember that he will return.