The office of the Mass, says Durandus, is devised with great forethought, so as to contain the major part of what was accomplished by and in Christ from the time when He descended from heaven to the time when He ascended into heaven. In the sacrifice of the Mass all the sacrifices of the Ancient Law are represented and superseded. It may be celebrated at the third hour, because then, according to Mark, Christ ascended the cross, and at that hour also the Holy Spirit descended upon the Apostles in tongues of fire; or at the sixth hour, when, according to Matthew, Christ was crucified; or at the ninth hour, when on the cross He gave up His spirit. The first part of the Mass begins with the _introit_. Its antiphonal chanting signifies the aspirations and deeds, the prayers and praises of the patriarchs and prophets who were looking for the coming of the Son of God. The chorus of chanting clergy represents this yearning multitude of saints of the Ancient Law. The bishop, clad in his sacred vestments,[85] at the end of the procession, emerging from the sacristy and advancing to the altar, represents Christ, the expected of the nations, emerging from the Virgin’s womb and entering the world, even as the Spouse from His secret chamber. The seven lights borne before him on the chief festivals are the seven gifts of the Holy Spirit descending upon the head of Christ. The two acolytes preceding him signify the Law and the Prophets, shown in Moses and Elias who appeared with Christ on Mount Tabor. The four who bear the canopy are the four evangelists, declaring the Gospel. The bishop takes his seat and lays aside his mitre. He is silent, as was Christ during His early years. The Book of the Gospels lies closed before him. Around him in the company of clergy are represented the Magi and others. The services proceed, every word and act filled with symbolic import. The reading of the Epistle is reached--that is the preaching of John the Baptist, who preaches only to the Jews; so the reader turns to the north, the region of the Ancient Law. The reading ended, he bows before the bishop, as the Baptist humbled himself before Christ. After the Epistle comes the Gradual or _responsorium_, which relates to penitence and the works of the active life. The Baptist is still the main figure, until the solemn moment when the Gospel is read, which signifies the beginning of Christ’s preaching. The Creed follows the Gospel, as faith follows the preaching of the truth. Its twelve parts refer to the calling of the twelve apostles. Then the bishop begins his sermon; that is to say, after the calling of the Twelve, the Word of God is preached to the people, and it henceforth behoves the Church to hold fast to the Creed which has just been recited.[86]