{57} The grades are given as follows in the Cor. Jur. Can., Dist. LXXVII, c. i. The candidate for the office of bishop must first have been doorkeeper (_ostiarius_), then reader (_lector_), then exorcist (_exorcista_), then consecrated as an acolyte (_acolythus_), then subdeacon (_subdiaconus_), then deacon (_diaconus_), then priest (_presbyter_), and then if he is elected he may be ordained bishop. The law expressed in chap. iii, so thoroughly in the interests of the ambitious clergy of Rome, was not long observed, for it frequently happened that the bishop of some other city was chosen pope. But it was in accord with previous legislation. The church had early declared against the removal of a clergyman from one congregation to another. Thus the council of Nicæa, 325, in its fifteenth canon (cf. Hefele, Conciliengeschichte, I, pp. 418 f), "forbids bishops, priests, and deacons to move from one town (congregation) to another, because such a practice is against the rule of the church and has often caused disturbances and divisions between congregations. If any bishop, priest, or deacon disobeys this command and removes to another congregation, his action shall be illegal, and he shall be sent back to the congregation which he was serving." 35. The Petrine Theory as Stated by Leo I, 440-61. Migne, 64. Leo I (440-61) made frequent use of the Petrine theory. In brief this theory is that to Peter as the prince of the apostles was committed the supreme power over the church. To him the keys were intrusted in a special manner. In this consisted his primacy, his superiority over the other apostles. This primacy or first rank he communicated to his successors, the bishops of Rome, who, by virtue of being his successors, held the same primacy over the church and over all other bishops as Peter held over the other apostles. The passage on which this theory is based is found in Matt. 16:18 f: "And I say unto thee, That thou art Peter, and upon this rock I will build my church; and the gates of hell shall not prevail against it. And I will give unto thee the keys of the kingdom of heaven: and whatsoever thou shalt bind on earth shall be bound in heaven: and whatsoever thou shalt loose on earth shall be loosed in heaven." We offer the following detached passages from the works of Leo I to illustrate his conception of the theory. Col. 628. Our Lord Jesus Christ, the Saviour of the world, caused his truth to be promulgated through the apostles. And while this duty was placed on all the apostles, the Lord made St. Peter the head of them all, that from him as from their head his gifts should flow out into all the body. So that if anyone separates himself from St. Peter he should know that he has no share in the divine blessing.