“Greet all the brothers and sisters with a holy kiss.”
1 Thessalonians 5.21
The normal greeting of antiquity was the kiss. Since Paul finds it necessary to stress that, among the saints, it ought to be holy, it may have been abused.
The emphasis here is not on the kiss but on it being holy. He isn’t establishing a ritual; he’s making sure that all we do is characteristic of God’s holiness.