7 After this plucking up immediately the root of the evils, He says,
“Provide neither gold, nor silver, nor brass in your purses, nor scrip for your journey, neither two coats, neither shoes, nor yet a staff.”
He said not, “take them not with you,” but, “even if you can obtain them from another, flee the evil disease.” And you see that hereby He was answering many good purposes; first setting His disciples above suspicion; secondly, freeing them from all care, so that they might give all their leisure to the word; thirdly, teaching them His own power. Of this accordingly He quite speaks out to them afterwards, “Lacked ye anything, when I sent you naked and unshod?”
He did not at once say, “Provide not,” but when He had said, “Cleanse the lepers, cast out devils,” then He said, “Provide nothing; freely you have received, freely give;” by His way of ordering things consulting at once for their interest, their credit, and their ability.
But perhaps some one may say, that the rest may not be unaccountable, but “not to have a scrip for the journey, neither two coats, nor a staff, nor shoes,” why did He enjoin this? Being minded to train them up unto all perfection; since even further back, He had suffered them not to take thought so much as for the next day. For even to the whole world He was to send them out as teachers. Therefore of men He makes them even angels (so to speak); releasing them from all worldly care, so that they should be possessed with one care alone, that of their teaching; or rather even from that He releases them, saying, “Take no thought how or what you shall speak.”
And thus, what seems to be very grievous and galling, this He shows to be especially light and easy for them. For nothing makes men so cheerful as being freed from anxiety and care; and especially when it is granted them, being so freed, to lack nothing, God being present, and becoming to them instead of all things.
Next, lest they should say, “whence then are we to obtain our necessary food?” He says not unto them, “You have heard that I have told you before, 'Behold the fowls of the air;'” (for they were not yet able to realise this commandment in their actions); but He added what came far short of this, saying, “For the workman is worthy of his meat;” declaring that they must be nourished by their disciples, that neither they might be high minded towards those whom they were teaching, as though giving all and receiving nothing at their hands; nor these again break away, as being despised by their teachers.
After this, that they may not say, “Do you then command us to live by begging?” and be ashamed of this, He signifies the thing to be a debt, both by calling them “workmen,” and by terming what was given, “hire.” For “think not,” says He, because the labor is in words, that the benefit conferred by you is small; nay, for the thing has much toil; and whatsoever they that are taught may give, it is not a free gift which they bestow, but a recompence which they render: “for the workman is worthy of his meat.” But this He said, not as declaring so much to be the worth of the apostles' labors, far from it; God forbid: but as both making it a law for them to seek nothing more, and as convincing the givers, that what they do is not an act of liberality, but a debt.
Source: Homilies on the Gospel of St. Matthew (New Advent)