24 In reference, however, to the character of Novatian, dearest brother, of whom you desired that intelligence should be written you what heresy he had introduced; know that, in the first place, we ought not even to be inquisitive as to what he teaches, so long as he teaches out of the pale of unity. Whoever he may be, and whatever he may be, he who is not in the Church of Christ is not a Christian. Although he may boast himself, and announce his philosophy or eloquence with lofty words, yet he who has not maintained brotherly love or ecclesiastical unity has lost even what he previously had been.
Unless he seems to you to be a bishop, who— when a bishop has been made in the Church by sixteen co-bishops— strives by bribery to be made an adulterous and extraneous bishop by the hands of deserters; and although there is one Church, divided by Christ throughout the whole world into many members, and also one episcopate diffused through a harmonious multitude of many bishops; in spite of God's tradition, in spite of the combined and everywhere compacted unity of the Catholic Church, is endeavouring to make a human church, and is sending his new apostles through very many cities, that he may establish some new foundations of his own appointment.
And although there have already been ordained in each city, and through all the provinces, bishops old in years, sound in faith, proved in trial, proscribed in persecution, (this one) dares to create over these other and false bishops: as if he could either wander over the whole world with the persistence of his new endeavour, or break asunder the structure of the ecclesiastical body, by the propagation of his own discord, not knowing that schismatics are always fervid at the beginning, but that they cannot increase nor add to what they have unlawfully begun, but that they immediately fail together with their evil emulation.
But he could not hold the episcopate, even if he had before been made bishop, since he has cut himself off from the body of his fellow bishops, and from the unity of the Church; since the apostle admonishes that we should mutually sustain one another, and not withdraw from the unity which God has appointed, and says, “Bearing with one another in love, endeavouring to keep the unity of the Spirit in the bond of peace.” He then who neither maintains the unity of the Spirit nor the bond of peace, and separates himself from the band of the Church, and from the assembly of priests, can neither have the power nor the honour of a bishop, since he has refused to maintain either the unity or the peace of the episcopate.
Source: The Epistles of Cyprian (New Advent)