John Nelson Darby emphasizes the critical nature of separation within the church, arguing that leaving an assembly that falsely claims to represent the church is necessary to maintain the truth of God's testimony. He warns against the dangers of remaining in a body that does not reflect the Spirit of God, as it can lead to a loss of blessing and spiritual integrity. Darby acknowledges the complexity of situations where evil persists within a church, stressing that true unity must not be a cover for wrongdoing. He concludes that while separation may be painful, it is sometimes essential for spiritual health and obedience to God. Ultimately, he encourages prayer for those who remain in such assemblies, hoping for their restoration through God's grace.

I write rather because of the importance of the point than for any immediate occasion of circumstances: I mean leaving an assembly, or setting up, as it is called, another table. I am not so afraid of it as some other brethren, but I must explain my reasons. If such or such a meeting were the church here, leaving it would be severing oneself from the assembly of God. But though wherever two or three are gathered together in Christ's name, He is in the midst, and the blessing and responsibility, of the church are, in a certain sense also, if any Christians now set up to be the church, or did any formal act which pretended to it, I should leave them as being a false pretension, and denying the very testimony to the state of ruin which God has called us to render. It would have ceased to be the table of the people and testimony of God, at least intelligently. It might be evil pretension or ignorance; it might call for patience, if it was in ignorance, or for remedy, if that was possible: but such a pretension I believe false, and I could not abide in what is false. I think it of the last importance that this pretension of any body should be kept down: I could not own it for a moment, because it is not the truth. On the other hand, united testimony to the truth is the greatest possible blessing from on high. And I think that if anyone, through the flesh, separated from two or three walking godlily before God in the unity of the whole body of Christ, it would not merely be an act of schism, but he would necessarily deprive himself of the blessing of God's presence. It resolves itself, like all else, into a question of flesh and Spirit. If the Spirit of God is in and sanctions the body, he who leaves in the flesh deprives himself of the blessing, and sins. If, on the contrary, the Spirit of God does not sanction the body, he who leaves it will get into the power and liberty of the Spirit by following Him. That is the real way to look at it. There may be evil, and yet the Spirit of God sanction the body (not, of course, its then state), or at least act with the body in putting it away. But if the Spirit of God, by any faithful person, moves in this, and the evil is not put away, but persisted in, is the Spirit of God with those who continue in the evil, or with him who will not? Or is the doctrine of the unity of the body to be made a cover for evil? ... Suppose clericalism so strong that the conscience of the body does not act at all, even when appealed to; is a simple saint who has perhaps no influence to set anything right, because of this very evil, therefore to stay with it? What resource has he? I suppose another case. Evil goes on, fleshly pretension, a low state of things on all sides. Some get hold of a particular evil which galls their flesh, and they leave. Do you think that the plea of unity will heal? Never. All are in the wrong. Now this often happens. Now the Lord in these cases is always over all. He chastens what was not of Him by such as separation, and shows the flesh in detail even where, in the main, His name was sought. If the seceders act in the flesh, they will not find blessing. God governs in these things, and will own righteousness where it is, if only in certain points. They would not prosper if [they act in the flesh], but they might remain a shame and sorrow to those they left. If it be merely pride of flesh, it will soon come to nothing. "There must be also heresies among you, that they which are approved may be made manifest" (1 Corinthians 11:19). If occasion has been given in any way, the Lord, because He loves, will not let go until the evil be purged out. If I do not act with Him, He will (and I should thank Him for it) put me down in the matter too. He loves the church, and has all power in heaven and earth, and never lets slip the reins. I have not broken bread, nor should do it, till the last extremity: and if I did, it would be in the fullest, openest testimony that I did not own the others then to be the table of the Lord at all. I should think worse of them than of sectarian bodies, because having more pretension to light. "Now ye say we see". But I should not (God forbid!) cease to pray continually, and so much the more earnestly, for them, that they might prosper through the fulness of the grace that is in Christ for them.