In 1 Corinthians 10, the Apostle Saint Paul exhorts us to all agree with one another and let there be no divisions among us. Disunity, however, is a reality that we have to deal with. Our Lord says that weeds will grow alongside the wheat, and in the fifth chapter of Galatians, contentions, dissensions and sects are listed amongst the works of the flesh. The difficulty in unity is that even if a person where perfect in charity, it would only take his companions being imperfect to cause disunity and quarreling.
It can be very frustrating to be on the sidelines of a fight between Christian brethren who are acting in passions of anger. There does appear to be occasional break periods where a journal here, a blog there, a bishop over there, and so on, will scream the need to stop fighting and unite to (insert noble cause here).
Have you read the exhortations to stop arguing over issues like canonical jurisdiction to make a united Trad Catholic Voice. Like this call for Unity that Rorate Caeli Posted in January of last year.
Calls to unity can also be found from the Russian Orthodox, asking for an end to confrontation between Catholics and Orthodox and a relationship of solidarity so that we might fight relativism and secularism. (Like Archbishop Hilarion said during an address to the Sant’Egidio community on September 17 or extreme examples like Saint John Paul II inviting the leaders of the worlds religion to pray for and work towards the promoting of peace.) Some Eastern Catholics on the internet express upset (the self identified "Orthodox in Communion with Rome") that the West cannot just jettison 1000 years of theology in the name of unity and nuance the meaning out of Papal Supremacy so we can be united with the Orthodox again (thus betraying Christ, and the noble Eastern Catholic Martyrs and Confessors) . Father Laurent Cleenewreck, an Eastern Orthodox Priest, wants Christians to return to a pre-Nicene confession of the faith, so that all us Christians can stop fighting.
We have been exhorted to dwell in unity; so why do some Christians insist on fighting over dogma or practice?
Because these can be salvation issues.
When people unite at the expense of truth, they construct a new tower of Babel destined to not only fail, but to cause even greater disunity. Our faith is weak, or possibly dead, if we think our numbers will make a difference. God cares not for numbers, but faithfulness, even if the numbers are reduced to a remnant of "the remnant".
Should people remain silent if they believe (Insert dis-unifying belief here) will actually result in someone going to Hell? Admonishing the sinner has guidelines, we must not throw our pearls before swine, and Our Lord admonishes us to correct someone only so many times before (in effect) shunning them.
If a person is wrong about a belief being a salvation issue, it may be a salvation issue to them for if they violate their conscience and they would actually commit a soul-destroying mortal sin. “Then let us no more pass judgment on one another, but rather decide never to put a stumbling block or hindrance in the way of a brother. I know and am persuaded in the Lord Jesus that nothing is unclean in itself; but it is unclean for anyone who thinks it unclean. (Rom 14:13–15)”
How must we deal with salvation issues, whether we our or neighbor believes that X is a salvation issue? By supplying evidence with patience and charity.
The Rule of the Poor Knights provides an excellent outline for how we should speak, and not speak, in these inevitable disagreements in our fallen world.
“Do not give free play to wrath, do not bear anyone a grudge, do not nurse deceit in your heart, do not give a false greeting of peace, do not abandon charity…. Speak the truth with your heart and your lips, do not render evil for evil, do not wrong anyone, love your enemies, do not return insults or slander, but rather respond with benevolence towards our offenders” Chapter 4, The Instruments of Good Deeds.
Are we in the position to lay down the sword of truth if our friend wants to join the the Eastern Schism so we can avoid contention? Will we stay silent if a dogma of our Faith is questioned by a protestant standing next to us at a Pro-Life demonstration, because he is "basically a good person"? Are we going to let our friends go to Sedevacantist church with our blessing because they have been scandalized and are "traditional"? Should we stay silent if our family wishes to attend the illegal ordination of a priest who, upon ordination, would be suspended?
I hope to God that I be found not wanting for words then. "Love thy neighbor as thyself." If you believe something is necessary to do, or to avoid for your salvation, do not be silent because your words might stir up contention. “Do not think that I came to send peace upon earth: I came not to send peace, but the sword. For I came to set a man at variance against his father, and the daughter against her mother, and the daughter in law against her mother in law. And as a man's enemies shall be they of his own household.” Matthew 10:34-36
It only takes one mortal sin for a person to lose the grace of God. What if God's providence chose you to be the person to warn somebody about their impending spiritual suicide? So what if we have a united "Trad Front" if a quarter of those trads go to hell? So what if we have a united Christianity if a large segment of that rejects Dogma necessary for belief in order to be saved? And you won't avoid one day of warfare by different religious leaders pledging peace when God decides if we will have war or peace, lest we forget that the Angel of War is sent to punish those who reject the Gospel. I would hope that if I was in danger of losing my soul a friend would take the time to patiently and charitably correct me.
We can make our arguments firm, we can use strong evidence and even be forceful if need be, but we must always strive to do it in charity. If we cannot start with charity it is be better to stay silent, but not for unity’s sake, for God’s sake. "A judicious silence is always better than truth spoken without charity." ~St. Francis De Sales
We must always keep charity, and that is also a salvation issue.