William Burkitt on Romans 16:16

Observe here, How the apostle proceeds from greeting the saints at Rome himself, to persuade them to salute one another. There had been much dissension amongst them about meats and days; he therefore craves of them for the future to embrace each other with cordial love, and affectionate kindness, and, as a token and symbol of it, to salute one another with an holy kiss, the usual expression of friendship in those times.

The primitive Christians, at the end of their prayers, before the celebration of the sacrament, did salute one another with a kiss, and then the bread and cup was brought forth; and some observe, that it was done by the men apart, and the women apart. But this custom being afterwards abused, was generally laid aside. That which is lawful in its use, and innocent in its own nature, may and ought to be laid aside when it becomes matter of scandal and just offence.