Adam Clarke on Matthew 10:13

If that house be worthy - If that family be proper for a preacher to lodge in, and the master be ready to embrace the message of salvation.

Your peace - The blessings you have prayed for shall come upon the family: God will prosper them in their bodies, souls, and substance.

But if it be not worthy - As above explained.

Let your peace - The blessings prayed for, return to you. Προς υμας επιϚραφητω, it shall turn back upon yourselves. They shall get nothing, and you shall have an increase.

The trials, disappointments, insults, and wants of the followers of Christ become, in the hand of the all-wise God, subservient to their best interests: hence, nothing can happen to them without their deriving profit from it, unless it be their own fault.