"There is nothing more grievous than the sacrilege of schism....there can be no just necessity for destroying the unity of the Church." (St. Augustine)
"You shall not make a schism. Rather, you shall make peace among those who are contending." – Didache (late first – early second century)
In order to understand how to bring about the "full and visible unity of all Christ's followers", we have to think about how to mend schisms. And that means we have to understand the nature of schism. Earlier this year I wrote about schism here and more recently here. And two weeks ago I argued here that the sooner we start recognizing schisms for what they are, the sooner we will realize that they need to be mended.
Mending a schism requires, among other things, knowing which party is in schism, otherwise neither side will see any need to join the other side. The two parties might meet at the ecumenical dialogue table (which is good), but if each side believes itself to have equal claim to being the continuation of the one, holy, catholic and apostolic Church, then neither has reason to join the other party, all other things being equal. So the question I wish to consider now is this: In the event of a schism, which of the resulting groups is the continuation of the one, holy, catholic and apostolic Church, and which is in schism from the one, holy, catholic and apostolic Church? (Of course this question will not apply to cases in which a group that is already in schism divides again.)
One important criterion for determining which is the continuing Church is retention of the doctrine of the Apostles. The continuing Church must retain the doctrine of the Apostles. But the primary problem with this criterion taken by itself is that any heretic can claim that his interpretation is that of the Apostles. That is because taking this criterion in isolation eliminates the possibility of an authoritative body that can adjudicate between claims to have the Apostolic doctrine. Here's why. If doctrinal agreement is the only criterion for determining the identity of the Church, then suppose there is a split into group A and group B. Group A might form its 'authoritative body' which then rules that group B is heretical, and group B might form its 'authoritative body' which then rules that group A is heretical. There is nothing that gives group A's 'authoritative body' any more authority than that of group B's, and vice versa. And if groups A and B each split into additional groups, the same will be true. Even if groups A and B split into as many groups as there are persons in both groups, the same will be true. Each person can say, "My interpretation is that of the Apostles", and no one has any greater authority to say, "No you don't." Hence, taking this criterion by itself is an adoption of individualism, an ecclesiology intrinsically disposed to fragmentation upon fragmentation.
So there must be an additional criterion, because Christ did not leave His Church without a principle of unity. In the fathers of the Church we find an additional criterion: sacramental succession from the Apostles (which I discussed here). By 'sacramental' I mean "by means of a sacrament", in this case the sacrament of Holy Orders. (Orthodox and Catholic fully agree that there are seven sacraments, and that Holy Orders is one of them.) Doctrine as such is purely formal. But a sacrament is not wholly *formal*, but necessarily includes a material principle. Baptism, for example, requires water as the material principle of that sacrament. The reason why a purely formal principle cannot be the sole criterion for determining which party in the event of a schism is the continuation of the one, holy, catholic and apostolic Church is that Form is capable of multiple instantiations. But there can be only one "holy, catholic, and apostolic Church", for Christ has only one Bride. Therefore there must be a material principle of identity and continuity. And that material principle is sacramental succession from the Apostles through the laying on of hands by those having such succession. The sacrament of Holy Orders confers magisterial authority. But only one having this authority can administer this sacrament. In the early Church magisterial authority was always treated as something that was passed down from God the Father to Christ (cf. Matthew 28:18; John 17:2; Revelation 2:28), from Christ to the Apostles, and from the Apostles to the bishops through the laying on of hands (1 Tim 4:14; 2 Tim 1:6). Often the Church (including the laity) would nominate candidates to replace a bishop who had died, but bishops were always ordained by other bishops. This is why submitting to the sacramental magisterial authorities (i.e. the bishops) was described (see here) by St. Ignatius (d. 107 AD) as submitting to Christ.
With this criterion, we can answer our initial question. First, when there is a schism, and one party does not have Holy Orders, and the other does, the party not having Holy Orders cannot be the continuation of the one, holy, catholic and apostolic Church, even if in all other possible respects it retains the Apostles' doctrine. The party not having Holy Orders is in schism. St. Ignatius (d. 107), bishop of Antioch, writes, to the Trallians, "Without these three orders [bishop, priest, and deacon] you cannot begin to speak of a church."
Second, the charism that accompanies the sacrament of Holy Orders is conferred whether or not the conferral is in accordance with Church law. This is why although the priests and bishops in the Novatian and Donatists schisms had Holy Orders, they were not the rightful authorities in their respective dioceses. So, in the event of a schism where both parties have Holy Orders, the party whose Orders were not received in accordance with Church law is the party in schism.
Third, one of the Apostles was given a primacy over the others, for to him alone did Christ say, "Upon this rock I will build My Church", and "I will give to you (singular) the keys of the kingdom of heaven." (St. Matthew 16:18-19) (See, for example, my previous blog post.) This Apostle passed on this authority to his episcopal successor in the Holy See (i.e. St. Linus), and he to his episcopal successor (i.e. St. Cletus). That list of bishops in succession can be seen here. Whenever a heterogeneous organism is divided, the head of the organism determines where the original organism continues. The part detached from the head is in schism from the organism. So likewise, whenever there is a schism and both parties have legitimate Holy Orders, the party that remains in communion with the episcopal successor of St. Peter is the continuation of the one, holy, catholic and apostolic Church. (If both parties remain in communion with the episcopal successor of St. Peter, then the schism is internal and must shortly be either resolved or one party will break with the episcopal successor of St. Peter, for he will require the two parties to be reconciled.)
"I pray not only for them, but also for those who will believe in me through their word, so that they may all be one." (St. John 17: 20-21) Lord Jesus, may we heed your prayer. Give us the grace, humility and love to leave behind the schisms we have made, and be one with each other as you are one with the Father. In the name of the Father, and the Son, and the Holy Spirit. Amen.
"Let unity, the greatest good of all goods, be your preoccupation." - St. Ignatius of Antioch (Letter to St. Polycarp)