64. And why is the Hymn Trisagion, besides being sung by the two choirs, sung further within the holy Altar by the priests ministering in the Service ?
These two singings of the Trisagion (Symeon explains in his book on the Temple and Liturgy) “denote the concert and union of Angels and Men. Whence both within this hymn is sung by the Priests, and outside by the Clerks and Laity. For the Church of Angels and Men has become one through CHRIST” and particularly because this hymn the Church received from heaven.“

In the time of the sainted Proclus, Theophanes relates in his Chronicle, great earth quakes took place in Constantinople for four months space; so that the Byzantines, for fear, fled out of the city for refuge to what is called the Field ; and with the Bishop they betook themselves to supplications with tears before GOD. On one occasion then, the earth heaving, and all the people crying aloud, LORD, have mercy, earnestly, at the third hour, suddenly, in the sight of all, a certain young man was lifted up by divine power into the air, and heard a divine voice bidding him tell the Bishop and the people to make their litanies thus:
Holy GOD, holy Mighty, holy Immortal, have mercy on us
making no further addition. And the sainted Proclus having received this declaration, permitted the people to sing thus, and at once the earthquake ceased. And the blessed Pulcheria and her brother, awestruck at the miracle, gave orders throughout all the world for the Divine Hymn to be sung ; and from that time the custom has obtained in all the Churches to sing it daily to GOD.”

The miracle happened for the overthrow of the Patripassians, who held with intolerable blasphemy that the SON of GOD suffered even as GOD; for which reason these wretches used to say the Trisagion with that addition, “Who wast crucified for us.” And not only in the Liturgy, but in every service, the Church since those times uses the Trisagion as a preface, just as it was heard in the sky. “ Thenceforward” writes Nicephorus, Bk. xiv. ch. 46, “; CHRIST’S Church accepted it, and not only every day, but to speak generally, at every commencement of a hymn to GOD, she first recites this with open mouth.”;

65. I want to hear likewise the Prayer which during the singing of the Trisagion the priest says secretly.
During the chanting of the Trisagion, the priest entreats GOD to receive from our mouth, too, as from the celestial powers, this very GOD-taught Hymn. The Prayer is as follows:
Holy GOD, Who restest among the saints, Who art with the thrice holy cry celebrated by the Seraphim, and glorified by the Cherubim, and worshipped by every heavenly power ; who out of nothing didst bring all into being ; Who createdst man after Thine image and similitude, and adornedst him with every gift of Thine ; Who givest wisdom and understanding to him that asketh, and dost not overlook the sinner, but ordainedst repentance for salvation ; Who hast vouchsafed to us, Thy humble and unworthy servants, even at this hour, to stand before the glory of Thy holy Altar, and to present the worship and praise due to Thee : Do Thou, O Master, accept even from the mouth of us sinners the Thrice-holy Hymn, and visit us with Thy goodness. Pardon us every offence, voluntary and involuntary, and sanctify our souls and bodies, and grant us in holiness to worship Thee all the days of our life : by the intercession of the holy Mother of GOD, and of all the Saints, who from the beginning have pleased Thee.

66. You said that beside the choirs, the thrice-holy Hymn is sung also by the officiating priests. I pray you why, in some Liturgies, only seven Priests are invited, neither more nor fewer?

This is what goes commonly by the name of the Office of Seven Popes. However, the Divine or Holy Liturgy can be celebrated by as many priests as you may choose, and particularly in the Holy Metropolises of GOD, where, on each occasion, on every holy day of the LORD, and Feast day, the chosen company join in the Liturgy, with the choir of the church. Howbeit this number seven is very full of mystery; and in discoursing about the Prayer Oil, the Thessalonian, in his book on the Mysteries, adduces many reasons bearing likewise on the Liturgies, which we usually celebrate for the dead, praying for them the mercies of GOD, the kingdom of heaven, and the forgiveness of sins. “Seven Priests,” he says, “custom has made it usual to invite I suppose because of the gifts of the Spirit numbered in Isaiah under seven heads (Isa. xi. i 3); or because of those seven priests of the Law, who long ago blew their trumpets seven times round Jericho, by GOD’S command, and overturned the walls, so that these might destroy the wicked city, and the stout walls of the ramparts of sin (Josh. vi. 8 20) ; or as though the soul were dead, and in imitation of the Prophet, as over the child of that Shunammite, upon the priests praying seven times, they should raise it up, just as Elisha bowed himself seven times upon the child, and prayed seven times (2 Kings iv. 35) ; or as Elijah prayed seven times and again opened heaven which he had shut for their sins and brought down rain (i Kings xviii. 43 45) ; so these praying seven times should loose the drought of sin, and with Peter open heaven, having gotten the key of grace and the mercy The thrice-holy hymn is composed of passages of Scripture, namely, from the Hymn of the Seraphim, Holy, Holy, Holy, (Isa. vi. 3), and from the Davidic Psalm, “My soul thirsteth after Got), the mighty, the living one”; (Ps. xlii. 3), and “have mercy upon us,” taken straight from Scripture (Ps. cxliii. 2, Isa. xxxiii. 2).

The Holy Catechism of Nicolas Bulgaris