Moreover, the wall of the city signifies nothing else than the divine guardianship, which alone suffices, without other watches, or arms, or towers, to guard that city. "I," says God through Zechariah, "will be to it a wall of fire round about, and in glory I will be in the midst of it" (Zech. 2). A truly wondrous promise. "I," He says, "will be a wall of fire round about," to keep off enemies; "and I will be in glory in the midst of it," to make the citizens glorious. As though He should say: Fire burns and gives light; therefore I will burn the enemies, and I will enlighten the citizens; so shall I be a wall of fire round about, and a light of glory within. This St. John also explains a little later when he says: "And the city hath no need of the sun, nor of the moon, to shine in it; for the brightness of God hath enlightened it, and the Lamb is the lamp thereof" (Rev. 21). The brightness of God, like a sun, enlightens minds; the Lamb of God, Christ, like a lamp, enlightens bodies. Christ is called a lamp, not because a lamp is needed in the night, but by comparison with the divinity: otherwise, if the faces of the blessed will shine like the sun in the kingdom of God, as the Lord Himself says in Matthew (Matt. 13), how much more will the face of Christ enlighten the city of God, not as a lamp, but as the primal sun? And for this reason St. John adds that "there shall be no night there" (Rev. 21). There remains the street of the city, which comprises the whole space within the circuit of the walls.
This is the common dwelling of the heavenly citizens, and it is all pure gold—that is, charity burning and luminous—which will contain them all, and through which each will dwell in the others by the affection of pure love; and not only each in the others, but all in God, and God in all: for "he that abideth in charity, abideth in God, and God in him" (1 John 4). That this might come to pass, Christ the Lord asked the Father in that prayer which, as He was going to His passion, He poured forth while all the Apostles listened, saying: "But not for these only do I pray, but for them also who through their word shall believe in Me; that they all may be one, as Thou, Father, in Me, and I in Thee, that they also may be one in Us" (John 17).
O most blessed city, which, set upon the highest mountain, enjoy the purest air; you who are founded upon the rock, so that you rest upon everlasting firmness; whose gates gleam like pearls and stand ever open to those who enter; whose wall is God, who ever surrounds you with His protection and adorns you like a precious jasper stone; whose street is charity, brighter than all gold and whiter than all crystal, which makes all who dwell in you to be one heart and one soul, fills them with unspeakable joy, and establishes them in everlasting peace. My soul longs and faints for your streets (Ps. 83:3). For what is more desirable to one who labors and groans in the midst of a perverse nation, among false brethren, and in this very world, which lies wholly in wickedness, than to fly away to the place of sweetest peace, where charity alone reigns? When shall I come and appear before the face of God? (Ps. 41:3) For what is sweeter to a soul that loves the Lord than to see the Beloved, and to be seen by the Beloved, and through a most intimate and delightful bond to dwell in Him and to be dwelt in by Him? It seems indeed an intolerable boldness that dust and ashes should sigh after your courts, O holy city; and a still greater boldness that a lowly little soul should aspire to the embrace of the supreme Creator; but He who gave that boldness will excuse it — He who asked the Father that we might all be one, and that as the Father is in the Son and the Son in the Father, so we also might be one in Them both.