Charles Ellicott Commentary Matthew 10:13

"And if the house be worthy, let your peace come upon it: but if it be not worthy, let your peace return to you." — Matthew 10:13 (ASV)

If the house is worthy — The doubt implied in the “if” seems at first somewhat inconsistent with the assumption that they only went into a house after having determined the worthiness of the occupant. It must be remembered, however, that the missionaries entered each city or village as strangers, and in such a case, even the most careful inquiry might not always be successful.

Let your peace come upon it — This means the peace implied in the greeting. The command is not so much an instruction addressed to them as it is the proclamation of an edict from the King in whose name they went. Their greeting was not to be a mere ceremonial form. It would be a real prayer wherever the conditions for peace were met on the other side. At worst, the prayer for peace would bring a blessing on the one who prayed.