Α. The schismatics

Schismatics have the same faith as the One Church. They were however excised - severed - from Her, for secondary reasons: "for certain ecclesiastic reasons and mendable issues ............. among them"  (Canon 1 of Basil the Great). Schismatics are the Old Calendarists in Greece.

Β. Conventiclers

Related to schismatics are conventiclers. These are the Bishops and Presbyters who - albeit unfrocked for misconduct - did not show obedience to the Church but instead continued to officiate, drawing even faithful people along with them, thus creating their own Church (Canon 1 of Basil the Great and Canon 31 of the holy Apostles).

C. Creating a schism: the worst of sins.

The holy pope Pelagius II (579-590 A.D.) says: The creation of a schism in the Church is a sin far weightier than denying Christ!  With apostasy, only one individual is accountable: the apostate.  With the creation of a schism, not only is the one who caused the schism accountable, but also all those who follow him. (Ref. Metropolitan Meletios of Nikopolis, p.130)

There are sins that are not forgivable, neither "in the present age nor in the age to come" (Matthew 12:32). And the creator of a schism remains unforgivable, forever! His sin is not forgiven, not even with with precious martyrdom! "Not even the blood of martyrdom is able to erase this sin" opines saint John the Chrysostom (Ρ.G. 57.250). This was why Saint Lucillian tossed into the streets the remains of a schismatic martyr!

A schismatic is cut off from the Church, but he still preserves the same faith as Her. And those who followed him had also preserved the faith immaculate. A heretic is both disfellowed from the Church and also has an erroneous faith. Thus, those who followed him had likewise lost the faith!  He had become the cause for seducing many away from the path of the Lord (Deuteron.13:5-7). So, if a schismatic who has divided the Church is not forgiven - not even with martyrdom - then how can a heretic - who has divided the Church and has also altered the faith - be forgiven?

D. The most glorious martyrdom.

On the basis of the aforementioned, one should suffer everything in order that the Church of Christ not be divided - as saint Dionysios of Alexandria had written to Bishop Navatus (Pedalion - the Rudder - p.33, footnote 2).  And the struggles that one must persevere in - so that the Church is not split - is far more pleasing to God; even more than the martyrdom that one would suffer, for the sake of not denying Christ. When he undergoes martyrdom, it is for his own benefit, whereas when he struggles for the Church to not be divided, then he is struggling for the sake of the entire Church!

Therefore, if the struggles of the one who strives so that the Church is not split apart count as martyrdom, then how are the struggles to be regarded of the one who strives for both the Church to remain intact and the faith be preserved immaculate?

Ε. The great martyrs holy fathers.

With the above in mind, the most holy fathers in their sacred struggles against heretics strove - above all else - so that the Church not be split apart. That is why:

a. They showed tolerance.

1. Saint Cyril of Alexandria in his letters does not taunt the heresy leader Nestorius; he does not sling abuse at him. On the contrary, he addresses him in a very flattering manner! He would write "Your reverence" or "your God-fearing person".  And he himself would explain that "we do not immediately apply a blade and fire to wounds, but wait for the suitable moment" (Migne 77, 124-125). He tried in this manner both to win that person in Christ, and also to not split the Church. That was how that major pillar of Orthodoxy acted!  (One can only wonder, how many must have taunted him as a traitor at the time...)

 2. Theodore of Mopsuestia was a heretic. Yet several Orthodox Bishops commemorated him in the "diptychs" during the Divine Liturgy!  And Saint Cyril of Alexandria - for the sake of the Church not becoming divided - kept "communion" with those bishops!  (Migne 99:1085)

3. When Saint John the Chrysostom was unfairly defrocked by the illegitimate Synod of Drys, forty of his bishop friends refused "communion" with his successor, the Elder Arsakios. However, in spite of his burning in the furnace of injustice, Saint John exhorted his bishop friends to "commune" with his successor so that the Church would not be divided!  "Commune, so that you do not split the Church, but do not sign"  (Migne 47:27-28).

 4. And even more extraordinary:  The Filioque heresy appeared in the West during the 6th century A.D.. And yet! The Eastern Church had tolerated the West with its Filioque for centuries (!) for the sake of not splitting the Church!!

b. They "played politics".

Furthermore, in their heroic struggle to preserve the Faith intact and the Church undivided, the holy Fathers would become "as prudent as snakes and pure as doves" (Matth.10:16, cmp. Luke 16:8)

Basil the Great never directly confessed the divinity of the Holy Spirit. Being divinely wise, he implemented his own "politics". If he had confessed it, he would have exacerbated the Arians and they, with the help of secular authority, would have taken over his Archbishop's throne.  And that would have imperiled the Faith. (Pedalion, p.53)

Something similar was implemented by the Apostle Paul in Athens. He had referred to Christ as "a man confirmed by God"  (Acts 2:22). And if his sermon were to be heard by a Christian with "mindless zeal" (Romans 10:2), then he would surely have accused the Apostle of being .... a Jehovah's Witness!  But the Apostle had his reasons. He was implementing a manoeuver: It was not yet time to speak of Christ's divinity. It sufficed for the time being for the Athenians to believe that Christ was a man, and that He had risen from the dead. (Saint John the Chrysostom, Homily 3,4 - On John)

Likewise Saint Kosmas the Aetolian - who had daily contact with followers of the anti-Christian Mohammed - would occasionally see his compatriots denying Christ to worship Mohammed; but even though this broke his heart, our saint would not make any direct attack against Mohammed!  This was out of prudence, not cowardice.  He left the Holy Mountain and went down into the world in order to curb the apostasy of his Christian compatriots.  If he had openly fought against Mohammed, the Turks would have immediately decapitated him. He would of course had become a martyr immediately, but his salvific mission would have been cut short.  

And yet, how many at the time had accused this great pillar of Orthodoxy as a coward! And even as a heretic!

And something even more scandalous:

During the era of Arianism, a few Orthodox Bishops had publicly confessed that they were Arians. Their logic: If they had publicly confessed Orthodoxy, they would have been removed from their thrones and heretic Bishops would have taken their place, in which case, the Faith would have been in danger.  Therefore, in order to save the Faith, they feigned Arianism and remained on their thrones. However, they would secretly ordain Orthodox priests and thus support Orthodoxy.  After the Arian disputes had finished, the Church also discussed this issue: whether those Bishops should be defrocked or not.  They were commended!  And they were left on their thrones!!  (see the book by Epiphanios Theodoropoulos "Articles, Studies, Letters" - Vol.A', Athens 1981, pp.222-223).

F. Conclusions.

In war, strategy is everything. And the battle - the fight for the Faith - requires strategy. That is what the ingenious holy Fathers did and saved the Faith.  War without strategy leads to a debacle. And battling for the Church without any strategy will lead to damages to the Church. 

What deception! We struggle to benefit the Church, but in essence we are struggling how to harm Her!

Heresies and schisms exist, "so that the tested ones are made manifest"  (1 Cor.11:19)