‘Salute all the brothers with a holy kiss.'
There is no certain instance in the Bible of a kiss being used in salutation except between family members. It was used between close family members and in order to demonstrate affection, as well as as a sign of submission to a superior. In Palestine kissing did not normally take place on the lips (but see Proverbs 24:26, which was however figurative and had in mind the kiss between lovers - Song of Solomon 1:2 compare Proverbs 7:13) and it was used usually between members of the same sex, although Jacob greeted his cousin Rachel with a kiss of greeting on their first meeting (Genesis 29:11). It would usually be on the cheek, the forehead or the beard, although for submission might be on hand or foot. Thus the idea of the kiss here is because he looked on ‘all the brothers' as brothers, members of his family the church. It was probably passed on by word of mouth rather than actually.