We typically think of separation between Christians in negative terms because it typically involves an implied or explicit rebuke by the one initiating the separation.
Separation can take place over denial—separating from those who claim to be Christians but obviously deny the gospel through heresy or evil works (e.g., Rom 16:17–18; Titus 1:10–16).
Separation can take place over disobedience—separating from those who indeed are Christians but are clearly disobeying a specific command in Scripture (e.g., 2 Thess 3:6, 15).
Separation can also take place over disagreement—separating from Christians whose approach to ministry widely differs from one’s own, or even separating from Christians whose character or background suggests a certain unfitness for ministry and thus joining in ministry together. Paul’s separation from Barnabas over John Mark would be an example of this (Acts 15:36–41).
But what if we see Christians separate from one another but do not make their reasons clear to others? And what if this separation is all the more obvious because those separating are in positions of leadership? How should we think about the matter?
First, using the categories above, if there is no public statement by one party about the other, we should assume that neither denial or disobedience are involved. Scripture commands us to “mark” and identify a heretic as necessary in order to avoid him in the future (Rom 16:17). We are likewise to silence and sharply rebuke false leaders who deny the gospel through their works (Titus 1:11, 13). While it is not exactly the same situation, we are to treat disobedient brothers in a similar manner—the “brothers” are commanded to keep away from the specific “brother” who is violating the Word of God (2 Thess 3:6, 15). Whether denial or disobedience, some sort of public rebuke is given through word and act. If one party or the other has not identified the other as denying the gospel or disobeying the clear commands of Scripture in some way, it could be slander and gossip on our part to assume and suggest otherwise.
This being the case, second, if two Christians part ways but say nothing publicly about the matter or about the other person, we could maybe assume that their separation is one of disagreement. The disagreement could be over how to approach a specific ministry or over one’s ministry philosophy as a whole. Leaders may part ways over mistakes or misjudgments that are not necessarily sins but have nonetheless led to disappointment and a lack of confidence in the other’s wisdom over time. Perhaps a leader asks another to carry out a significant task that the other feels he is not gifted or skilled to complete, so the second man chooses to move on to another ministry where he believes can effectively serve.
With that last thought in mind, third, sometimes a separation between leaders involves no denial, disobedience, or disagreement at all. For the sake of continuing our alliteration, perhaps we could call this separation divine, that is, that it is God who is the One who providentially brings the separation about. It may simply be that, whereas the Lord gave someone a specific ministry for a time, the Lord may create an opportunity for someone to move on and serve somewhere else. It is always sad for brothers to part, even for good reason, when God chooses to move someone from one ministry to another (cf. Acts 20:37; 2 Tim 1:3).
Considering the above, we should guard ourselves from automatically assuming that a parting of ways involves sin, mistakes, or even disagreement. If a denial of the gospel is involved, it is the responsibility of the true Christian to make this denial known as necessary. If disobedience is involved, the obedient Christian is responsible to act accordingly. If disagreement is involved, perhaps the reasons may be stated, and perhaps they may be not. And sometimes a parting of ways simply comes about by the clear and remarkable providence of God.