7 But lest any should fancy that this was granted only to the twelve, see also what Luke relates: “After these things,” says he, “the Lord chose also other seventy and two, and sent them by two and two before His face into every city and place whither He was about to come. And He said unto them, The harvest indeed is plentiful, but the laborers few: ask ye therefore the Lord of the harvest, that He would send forth laborers into His harvest. Go your ways: behold, I send you as lambs in the midst of wolves.
Carry neither purse nor scrip nor shoes, and salute no man by the way. Into whatsoever house you shall enter, first say, Peace be to this house. And if the son of peace be there, your peace shall rest upon him: if not, it shall return to you. And in the same house remain, eating and drinking such things as are with them: for the workman is worthy of his hire.” Here it appears that these things were not commanded, but permitted, that whoso should choose to use, might use that which was lawful unto him by the Lord's appointment; but if any should not choose to use it, he would not do contrary to a thing commanded, but would be yielding up his own right, by demeaning himself more mercifully and laboriously in the Gospel in the which he would not accept even the hire which was his due.
Otherwise the Apostle did contrary to a command of the Lord: for, after he had shown it to be lawful unto him, he has straightway subjoined, “But yet have I not used this power.”
Source: On the Work of Monks (New Advent)