Adam Clarke on 1 Thessalonians 5:12

Know them - Act kindly towards them; acknowledge them as the messengers of Christ; and treat them with tenderness and respect. This is a frequent meaning of the word γινωσκω. See on Joh 1:10 (note).

Them which labor among you - The words τους κοπιωντας have appeared to some as expressing those who had labored among them; but as it is the participle of the present tense, there is no need to consider it in this light. Both it and the word προΐσταμενους, the superintendents, refer to persons then actually employed in the work of God. These were all admonishers, teachers, and instructers of the people, devoting their time and talents to this important work.