A common objection against the practice of separation from brothers in Christ is that separation implies the brother is in sin and no true Christian can remain in sin. If the fundamentalist (here defined as an orthodox Christian who practices the doctrines of separation from both false teachers and persistently disobedient brothers both within and beyond the local church) grants this objection, he is forced either to concede that his evangelical brothers’ failure to practice separation is not sinful or he is forced to conclude that evangelicals are, in fact, not truly brothers at all.

While this objection must be (and can be) met on exegetical and theological grounds, parallel situations in church history often helpfully shed light on present debates.

An example of this may be found in the discussions about unification between the northern and southern Presbyterian churches after the Civil War. In these discussions B. B. Warfield recognized both that different sins required differing levels of responses and that in certain situations a sin may require ecclesiastical separation without casting doubt on the professed salvation of those separated from.

Note this letter from Warfield to a fellow Presbyterian pastor in 1887:

I must confess to you that I am one of those whom you perhaps consider grossly inconsistent, who heartily accord with both the deliverances of 1818 & 1845. I do think slavery a gigantic evil & entirely inconsistent with the spirit of the Gospel & a sin in the slave holders: & I do not think it a disciplinable offense or a fit test of communion. It is possible ‘to sin against Christ’ & yet not be subject to exclusion from his table (1 Cor. viii. 12, compared with the context & the parallel in Romans xiv, e.g. Ro xiv 3). . . .
. . . That the Southern Church has not repented of its sin in regard to slavery would be no bar to my union with it: I could unite with it in a free conscience tomorrow. But that it is not awake to its duty to the Freedman & that organic union with it would injure if not destroy our work among them makes me deprecate & pray against reunion in any near future.

Cited in Bradley J. Gundlach, “Warfield, Biblical Authority, and Jim Crow,” in B. B. Warfield: Essays on His Life and Thought, ed. Gary L. W. Johnson (P&R, 2007), 163.

In other words, Warfield insisted on remaining ecclesiastically separate from R. L. Dabney, but he was not casting doubt on the intransigent Dabney’s regeneration.

“The first thought of the godly man in every circumstance is God’s relation to him and it, and his and its relation to God. That is God-consciousness and that is what the fear of God entails.”

John Murray, Principles of Conduct, 238

Exodus 20:20 intrigues the attentive reader with an interesting juxtaposition of ideas. The delivery of the Decalogue with its accompanying theophanic thundering, lighting, trumpeting, and smoking supplies the context for the verse. The people were afraid, and they moved from the foot of the mountain (19:17) to a place “far off” (20:18) (Currid, 2:53). They pled with Moses to serve as their mediator because they feared God would strike them dead.

Exodus 20:20 is Moses’ response to these fears. He first of all rebukes the people for their fear: “Do not fear.” He explains to them the cause of God’s coming (marked by the כִּי). God came to test them, not to kill them. Furthermore, God intended this test to produce fear(!) in the people.

At Sinai God came to test his people in a way that should remove one kind of fear and should instill another kind of fear.

This raises the question of how God’s coming at Sinai was a test for the people. Similar occurrences of the word “test” [נִסָה] (Gen 22:1; Ex 15:25; Ex 16:4; Deut 8:2; Deut 8:16; Deut 13:3; Judg 2:22; Jdg 3:1; Jdg 3:4; Ps 26:2) indicate that God tests his people to reveal if they will obey him (in Deut. 13:3 the test reveals whether or not they love him). But the purpose [וּבַעֲבוּר] of this test, at least as stated in this verse, is not to reveal something but to produce something: people that fear God in such a way that they do not sin.

Helfmeyer, following Noth, says “The people assembled at Sinai passed the test: they ‘have shown the right ‘fear’ of God and have not attempted to go too near the theophany” (TDOT, 9:451; cf Stuart, NAC, 469). This, however, misses Moses initial statement, “Do not fear.”

The children of Israel seemed to have failed this test. The test revealed in their hearts a fear that drove them from God. It should have produced a fear that drove them closer to God. The fear God intended to produce by the test at Sinai included the idea of dread (with Stuart, NAC, 469; against Currid, 54, who downgrades the term to mere “reverence”) because the fear of God includes fear of judgment (cf. Ex. 20:5; Deut 17:13; 21:21; Matt. 10:28; Heb. 4:1; 10:27, 31; cf. John Murray, Principles of Conduct, 233f.). But right fear of God–the kind of fear not forbidden–is more extensive than mere dread. As John Murray says, “The fear of God in which godliness consists is the fear which constrains adoration and love. It is the fear which consists in awe, reverence, honour, and worship, and all of these on the highest level of exercise” (Principles of Conduct, 236; cf. Deut 6:2 with 6:5; Deut 10:12; Josh 24:14; 1 Sam 12:24; Psalm 112:1; Pro 8:13).

The fear that the test at Sinai should have produced is modeled by Isaiah in the sixth chapter of his book. There he combined “Woe to me, for I am destroyed” (6:5) with “Behold me; send me” (6:8). Implicit in God’s command for Israel not to fear so as to draw back but to fear so as not to sin is the promise of mercy enacted in Isaiah 6:6-7. For those with ears to ear, Exodus 20:20 was a promise to Israel that God would provide atonement for their sin.