For this reason both the wall is built of this stone and, according to Isaiah, the city’s stronghold is adorned with it; see Isa 54:12. Moses speaks of the color and meaning of this stone when he describes the house of God: “Under His feet there was something like a work of pure sapphire, and like the very heaven in clarity” (Ex 24:10). Ezekiel also declares that the place on which the throne of God stands is as though made of sapphire; see Ezek 1:26; 10:1. The glory of God dwells in this color, which bears within itself the image of what is above the heavens. Any person like it can cry out with the apostle: “Our citizenship is in heaven” (Phil 3:20). Pierced by the rays of the sun, sapphire bursts forth in dazzling radiance. So too the mind of the saints always attends to heavenly things. Daily renewed by the rays of divine light, it eagerly and fervently seeks the eternal by every means and urges others to seek it. For when it is said that what happened at the Red Sea will happen again, this means that through the Lord’s sufferings and the washing of holy baptism, the mind of mortals is lifted upward, already tasting heavenly things. Chalcedony is difficult to see, like the weak flame of a lamp, and it shines not in a house but under the open sky. So too are those who, sustained by longing for heaven, remain unknown to men and, as though hidden from them, live by fasting, almsgiving, and prayer. Yet when they are commanded to come forth to men, whether for teaching or for some other ministry of the saints, they immediately reveal their inner radiance to the world. And the fact that chalcedony is found among the Nasamones, that is, in an Ethiopian province, speaks to us of people surrounded by the burning heat of love. Yet there is a certain strange opinion that this stone is dark, like dark skin. Emeralds are of different kinds, but the noblest is the Scythian, then the Bactrian, and in third place the Egyptian. Emerald signifies souls always strong in faith. The more the trials of this age, symbolized by Scythian cold, press upon them, the more firmly they cling to the eternal and unfading inheritance kept in heaven. These souls gather the mind and satisfy the thirst of their neighbors by preaching. Though despised by the world, they advance by the cup of the Lord’s sufferings and by the fullness of inner love granted them by the Holy Spirit.