Moreover, the foundation of this city is of such a kind that this city alone can deservedly be said to have a foundation. For so speaks the holy Apostle in the Epistle to the Hebrews: "For he looked for a city that hath foundations, whose builder and maker is God" (Heb. 11). For the Apostle gives the reason why Abraham built neither a city nor a house in the land of promise, but dwelt in it as a stranger: the reason is that he understood that land of promise to be a kind of figure of a greater land of promise, and therefore he was unwilling to build a house or a city that would perish, because he was looking for a city resting upon a firm foundation, whose builder and maker is God. And so only the heavenly city truly and properly has a foundation, which, built by God, will endure forever: the cities that men built—Cain, Nimrod, Ninus, Nebuchadnezzar, Romulus, and the rest—by having so often fallen, and by being destined to be utterly destroyed at the consummation of the world, show plainly enough that they had no foundation. Hence we may understand how much wiser than we were those Patriarchs, who, though they lived more than twice as long as we live, and had to wait for several thousand years before entering the heavenly city, yet deigned to build neither cities nor houses, but chose to dwell in tents as pilgrims, remembering that an eternal home awaited them in heaven, and that all things on earth would shortly perish.
But we, who live for the briefest span of time, and who can, if we will, enter that heavenly and most blessed city immediately after death, labor so at erecting and adorning buildings on earth, as though either we were never to die, or did not look forward to the heavenly city. Surely in this matter we imitate not the believing Patriarchs, but the unbelieving heathen; and yet we are Christians, and we know that Christ and the Apostles wished to have on earth neither a city, nor a tower, nor even a house—much less to build one. Yet we do not reprove the princes of this world, though Christian, who build new cities, nor private persons who build comfortable houses for themselves and their families; for we know that David built a royal house for himself in that city, as holy Scripture teaches in the books of Kings (2 Sam. 5). We know likewise that St. Louis, king of the Franks, restored at his own expense several Christian cities in Palestine; nor are we unaware that it is fitting for princes to dwell more comfortably and magnificently than private persons, and for patricians than plebeians; but we demand moderation, and we condemn excess—above all when private men covet the palaces of kings, and kings, not content with palaces, build for themselves immense piles that rival towns in size. In short, we condemn excessive attachment to these temporal things, as though the highest good were placed in them, and we praise contempt of the world and the humility of Christ.
Now the gates of the City are said by St. John, in the place cited, to be made of pearls (Rev. 21), the fabric of the walls of jasper stone, and the street of the city—indeed the whole city—of pure gold. All of which signifies that that holy city is wholly precious, yet bright and translucent: for pearls are precious, and so is jasper, of which one kind is green and another white. And for this reason St. John says: "And the light thereof was like to a precious stone, as to the jasper stone, even as crystal"—for he added "even as crystal" to show that he spoke of jasper that is not green, or of some other color, but white and shining. So also, when he said that the street was of pure gold, he added "as it were transparent glass," that is, clear and gleaming white like crystal. And so that whole city, whether you look upon its gates, its walls, or its streets, is precious; it admits nothing cheap, nothing base, nothing perishable; and at the same time it is all bright and all transparent, because nothing covered, nothing closed is found there—all see all things; there is no suspicion there, no deceit.
And perhaps this is the reason why St. John says in the same place: "And the gates thereof shall not be shut"—because there is no darkness there, no thieves, no enemies, on account of which doors are shut at night. Nor does this conflict with the words of the Psalmist, who sings in praise of the heavenly city: "Praise the Lord, O Jerusalem, because he hath strengthened the bolts of thy gates" (Ps. 147). For both the Prophet and the Evangelist wished to signify one and the same thing: that the city on high is in no danger from enemies or thieves. The one signified it by doors ever shut, the other by doors ever open: for the former, by doors ever shut, signified that the divine protection would never suffer any enemy to enter that city beloved of God; the latter, by doors ever open, signified that the city is so secure from every evil assault that there is no need to shut its gates, much less to post guards. But what the gate, the wall, and the street signify is that after Christ's passion an entrance was given to men for entering into the city of God and of the Angels: for Christ Himself, having vanquished the sting of death, opened the kingdom of God to believers. Nor is there one gate only, but twelve, through which the faithful may enter that city. For so speaks St. John: "On the east, three gates; and on the north, three gates; and on the south, three gates; and on the west, three gates" (Rev. 21). For not only Jews enter, as they fancy, but all nations from every part of the world; indeed, so few Jews enter that in comparison with the rest they can be called almost none. For so the Lord foretold to them when He said of the centurion: "I have not found so great faith in Israel. And I say to you that many shall come from the east and the west, and shall sit down with Abraham, and Isaac, and Jacob in the kingdom of heaven; but the children of the kingdom shall be cast out into the exterior darkness" (Matt. 8). And in the parable of the vineyard: "The kingdom of God shall be taken from you, and shall be given to a nation yielding the fruits thereof" (Matt. 21). And most clearly in Luke: "When you shall see Abraham, and Isaac, and Jacob, and all the prophets in the kingdom of God, and you yourselves thrust out. And there shall come from the east, and the west, and the north, and the south, and shall sit down in the kingdom of God" (Luke 13).
Now three gates are said to stand on every side of the world—twelve in all—because access will be open not only from the east, the north, the west, and the south, but from the beginning of the east, the middle of the east, and the end of the east, and so likewise for the other quarters of the world. Unless it be more pleasing to think that three gates are assigned to each side of the heavenly city on account of the mystery of the Trinity and of the three most necessary virtues: for all those enter from the four quarters of the world who, baptized in the name of the three divine Persons, have kept faith, hope, and charity even to the end.