4 Now these things were enough to recommend men to receive them, their appointed healers. Yea, who would choose but receive with all readiness them that were so noble, such true heroes, and as lions running about the earth, and despising all that pertained to themselves, so that others might be saved? Yet nevertheless He proffers also another reward, indicating that He is caring here for the entertainers more than for the guests.
And the first honor He confers is by saying,
“He that receives you, receives me, and he that receives me, receives Him that sent me.”
With this, what may compare? That one should receive the Father and the Son! But He holds out herewith another reward also.
“He,” says He, “that receives a prophet in the name of a prophet, shall receive a prophet's reward; and he that receives a righteous man in the name of a righteous man, shall receive a righteous man's reward.”
And as before He threatens punishment to such as do not receive them, here He defines also a certain refreshment for the good. And to teach you His greater care for them, He said not simply, “He that receives a prophet,” or “He that receives a righteous man,” but subjoined, “in the name of a prophet,” and, “in the name of a righteous man;” that is, if not for any worldly preferment, nor for any other temporal thing, he receive him, but because he is either a prophet or a righteous man, he shall receive a prophet's reward, and a righteous man's reward; such as it were meet for him to have, that has received a prophet, or a righteous man; or, such as that other is himself to receive. Which kind of thing Paul also said: “That your abundance may be a supply for their want, that their abundance also may be a supply for your want.”
Then, lest any one should allege poverty, He says,
“Or whosoever shall give to drink unto one of these little ones a cup of cold water only in the name of a disciple, verily I say unto you, he shall in no wise lose his reward.”
“Though a cup of cold water be your gift, on which there is nothing laid out, even of this shall a reward be stored up for you. For I do all things for the sake of you the receivers.”
Do you see what mighty persuasions He used, and how He opened to them the houses of the whole world? Yea, He signified that men are their debtors: first, by saying, “The workman is worthy of his hire;” secondly, by sending them forth having nothing; thirdly, by giving them up to wars and fightings in behalf of them that receive them; fourthly, by committing to them miracles also; fifthly, in that He did by their lips introduce peace, the cause of all blessings, into the houses of such as receive them; sixthly, by threatening things more grievous than Sodom to such as receive them not: seventhly, by signifying that as many as welcome them are receiving both Himself and the Father; eighthly, by promising both a prophet's and a righteous man's reward: ninthly, by undertaking that the recompenses shall be great, even for a cup of cold water. Now each one of these things, even by itself, were enough to attract them. For who, tell me, when a leader of armies wounded in innumerable places, and dyed in blood, came in sight, returning after many trophies from war and conflict, would not receive him, throwing open every door in his house?
Source: Homilies on the Gospel of St. Matthew (New Advent)