John Calvin Commentary Matthew 10:12

"And as ye enter into the house, salute it." — Matthew 10:12 (ASV)

Salute it. As they could not distinguish the devout worshippers of God from scoffers, he enjoins them to address in a friendly manner any family they might encounter. The act of saluting is a kind of opening to a conversation. They had already been warned to look for people to host them, whose religious zeal was generally known and believed.

But as it sometimes happens that people with a high reputation, when brought to a serious test, reveal their impiety, it was fitting for this rule to be clearly stated.

The meaning therefore is: “Test, when you first enter, whether your hosts will cheerfully submit to hear you. Whoever willingly embraces your doctrine, remain in their house, so that your greeting may be confirmed. If any reject you, depart from them immediately and, as much as you are able, withdraw your greeting.”