“And as you enter into the house, salute it. And if the house is worthy, let your peace come on it, but if it is not worthy, let your peace return to you.”
As they entered the house that welcomed them they were to salute it, probably with the words ‘shalom elechem' (peace to you), a regular Jewish greeting. But in their case it would signify more, for they were the representatives of the Prince of Peace (Isaiah 9:7). Thus their granting of peace carried His authority with it. And if the house proved worthy, presumably by its response to their message, God would ensure that their words would then result in their own fulfilment. At their word God's peace would come on the house. Indeed all within it would find peace, for they would find it in response to the words of Jesus through the Apostles. But if the house did not respond to their message then it would be rejecting God's peace, and the peace would therefore return to them. The idea is probably that the disciples should take back their peace, either by leaving and going elsewhere, or by shaking their dust off their feet against them (Matthew 10:14), or indeed both. But in the end the message is that men are blessed by God, not on the basis of what they do, but on the basis of how they respond to Him in it.