Jamieson, Fausset and Brown on 1 Thessalonians 5:26

26. Hence it appears this Epistle was first handed to the elders, who communicated it to "the brethren."

holy kiss--pure and chaste. "A kiss of charity" (1Pe 5:14). A token of Christian fellowship in those days (compare Lu 7:45; Ac 20:37), as it is a common mode of salutation in many countries. The custom hence arose in the early Church of passing the kiss through the congregation at the holy communion [Justin Martyr, Apology, 1.65; Apostolic Constitutions, 2.57], the men kissing the men, and the women the women, in the Lord. So in the Syrian Church each takes his neighbor's right hand and gives the salutation, "Peace."