12 For “the world” is the appellation given not only to this fabric which God made heaven and earth, the sea, things visible and invisible: but the inhabitants of the world are called the world, just as we call a “house” both the walls and them that inhabit therein. And sometimes we praise a house, and find fault with the inhabitants. For we say, A good house; because it is marbled and beautifully ceiled: and in another sense we say, A good house: no man there suffers wrong, no acts of plunder, no acts of oppression, are done there. Now we praise not the building, but those who dwell within the building: yet we call it “house,” both this and that. For all lovers of the world, because by love they inhabit the world, just as those inhabit heaven, whose heart is on high while in the flesh they walk on earth: I say then, all lovers of the world are called the world. The same have only these three things, “lust of the flesh, lust of the eyes, vain glory of life.” For they lust to eat, drink, cohabit: to use these pleasures. Not surely, that there is no allowed measure in these things, or that when it is said, Love not these things, it means that you are not to eat, or not to drink, or not to beget children? This is not the thing said. Only, let there be measure, because of the Creator, that these things may not bind you by your loving of them: lest you love that for enjoyment, which you ought to have for use. But you are not put to the proof except when two things are propounded to you, this or that: Will you righteousness or gains? I have not wherewithal to live, have not wherewithal to eat, have not wherewithal to drink. But what if you can not have these but by iniquity? Is it not better to love that which you lose not, than to lose yourself by iniquity? You see the gain of gold, the loss of faith you see not. This then, says he to us, is “the lust of the flesh,” i.e. the lusting after those things which pertain to the flesh, such as food, and carnal cohabitation, and all other such like.
13. “And the lust of the eyes:” by “the lust of the eyes,” he means all curiosity. Now how wide is the scope of curiosity! This it is that works in spectacles, in theatres, in sacraments of the devil, in magical arts, in dealings with darkness: none other than curiosity. Sometimes it tempts even the servants of God, so that they wish as it were to work a miracle, to tempt God whether He will hear their prayers in working of miracles; it is curiosity: this is “lust of the eyes;” it “is not of the Father.” If God has given the power, do the miracle, for He has put it in your way to do it: for think not that those who have not done miracles shall not pertain to the kingdom of God. When the apostles were rejoicing that the demons were subject to them, what said the Lord to them? “Rejoice not in this, but rejoice because your names are written in heaven.” In that would He have the apostles to rejoice, wherein you also rejoice. Woe to you truly if your name be not written in heaven! Is it woe to you if you raise not the dead? Is it woe to you if you walk not on the sea? Is it woe to you if you cast not out demons? If you have received power to do them, use it humbly, not proudly. For even of certain false prophets the Lord has said that “they shall do signs and prodigies.” Therefore let there be no “ambition of the world:” Ambitio sæculi, is Pride. The man wishes to make much of himself in his honors: he thinks himself great, whether because of riches, or because of some power.
Source: Homilies on the First Epistle of John (New Advent)