11 After this He leads on to another, a higher image.
“You are the light of the world.”
“Of the world” again; not of one nation, nor of twenty states, but of the whole inhabited earth. And “a light” to the mind, far better than this sunbeam: like as they were also a spiritual salt. And before they are salt, and now light; to teach you how great is the gain of these strict precepts, and the profit of that grave discipline: how it binds, and permits not to become dissolute; and causes clear sight, leading men on to virtue.
“A city that is set on a hill cannot be hid, neither do men light a candle, and put it under the bushel.”
Again, by these words He trains them to strictness of life, teaching them to be earnest in their endeavors, as set before the eyes of all men, and contending in the midst of the amphitheatre of the world. For, “look not to this,” He says, “that we are now sitting here, that we are in a small portion of one corner. For you shall be as conspicuous to all as a city set on the ridge of a hill, as a candle in a house on the candlestick, giving light.”
Where now are they who persevere in disbelieving the power of Christ? Let them hear these things, and let them adore His might, amazed at the power of the prophecy. For consider how great things he promised to them, who were not known even in their own country: that earth and sea should know them, and that they should by their fame reach to the limits of the inhabited world; or rather, not by their fame, but by the working of the good they wrought. For it was not fame that bearing them everywhere made them conspicuous, but also the actual demonstration by their works. Since, as though they had wings, more vehemently than the sunbeam did they overrun the whole earth, sowing the light of godliness.
But here He seems to me to be also training them to boldness of speech. For to say, “A city set on a hill cannot be hid,” is to speak as declaring His own powers. For as that city can by no means be hidden, so it was impossible that what they preached should sink into silence and obscurity. Thus, since He had spoken of persecutions and calumnies, of plots and wars, for fear they might think that these would have power to stop their mouths; to encourage them, He says, that so far from being hid, it should over-shine the whole world; and that on this very account they should be illustrious and renowned.
By this then He declares His own power. In what follows, He requires that boldness of speech which was due on their part; thus saying,
“Neither do men light a candle and put it under the bushel, but on the candlestick, and it gives light unto all that are in the house. Let your light so shine before men, that they may see your good works, and glorify your Father which is in Heaven.”
“For I,” says He, it is true, have kindled the light, but its continuing to burn, let that come of your diligence: not for your own sakes alone, but also for their sake, who are to profit by these rays, and to be guided unto the truth. Since the calumnies surely shall not be able to obscure your brightness, if you be still living a strict life, and as becomes those who are to convert the whole world. Show forth therefore a life worthy of His grace; that even as it is everywhere preached, so this light may everywhere accompany the same.
Next He sets before them another sort of gain, besides the salvation of mankind, enough to make them strive earnestly, and to lead them unto all diligence. As thus, “You shall not only,” says He, “amend the world, if you live aright, but you will also give occasion that God shall be glorified; even as if you do the contrary, you will both destroy men, and make God's name to be blasphemed.”
And how, it may be asked, shall God be glorified through us, if at least men are to speak evil of us? Nay, not all men, and even they themselves who in envy do this, will in their conscience admire and approve you; even as the outward flatterers of such as live in wickedness do in mind accuse them.
What then? Do you command us to live for display and vain glory? Far from it; I say not this; for I did not say, “Give ye diligence to bring forward your own good deeds,” neither did I say, “Show them;” but “Let your light shine.” That is, “Let your virtue be great, and the fire abundant, and the light unspeakable.” For when virtue is so great, it cannot lie hidden, though its pursuer shade it over ten thousand fold. Present unto them an irreprehensible life, and let them have no true occasion of evil speaking; and then, though there be thousands of evil-speakers, no man shall be able to cast any shade upon you. And well did He say, “your light,” for nothing makes a man so illustrious, how manifold soever his will to be concealed, as the manifestation of virtue. For as if he were clad with the very sunbeam, so he shines, yet brighter than it; not spending his rays on earth, but surmounting also Heaven itself.
Hence also He comforts them more abundantly. For, “What though the slander pain you,” says He; yet shall you have many to honor God on your account. And in both ways your recompence is gathering, as well because God is glorified through you, as because you are defamed for God's sake. Thus, lest we should on purpose seek to be reproached, on hearing that there is a reward for it: first, He has not expressed that sentiment simply, but with two limitations, namely, when what is said is false, and when it is for God's sake:— and next He signifies how not that only, but also good report, has its great profit, the glory of it passing on to God. And He holds out to them those gracious hopes. “For,” says He, the calumny of the wicked avails not so much as to put all others in the dark, in respect of seeing your light. For then only when you have “lost your savor” shall they tread you under foot; but not when you are falsely accused, doing right. Yea, rather then shall there be many admiring, not you only, but for your sake your Father also. And He said not “God,” but “your Father;” already sowing beforehand the seeds of that noble birth, which was about to be bestowed upon them. Moreover, indicating His parity in honor, as He said above, “Grieve not when you are evil spoken of, for it is enough for you that for my sake you are thus spoken of;” so here He mentions the Father: every where manifesting His equality.
Source: Homilies on the Gospel of St. Matthew (New Advent)