Jamieson, Fausset and Brown on 1 Thessalonians 5:25

25. Some oldest manuscripts read, "Pray ye also for (literally, 'concerning') us"; make us and our work the subject of your prayers, even as we have been just praying for you (1Th 5:23). Others omit the "also." The clergy need much the prayers of their flocks. Paul makes the same request in the Epistles to Romans, Ephesians, Philippians, Colossians, Philemon, and in Second Corinthians; not so in the Epistles to Timothy and Titus, whose intercessions, as his spiritual sons, he was already sure of; nor in the Epistles, I Corinthians, and Galatians, as these Epistles abound in rebuke.