A fifth characteristic of a deluded conscience is that it “is ordinarily bitter and cruel in the effects of it. As it is proud and vain, so it will persecute to the death them it differs from; hence were the persecutions of the apostles and of Paul especially. And we have seen it in poor deluded souls, who have thought themselves obliged to slay all that were against them or differed from them in these their delusions. Somewhat of this bitter spirit accompanied the delusion of the Galatians. Therefore the apostle says to them (Gal 5:15) If ye bite and devour one another, etc. And James speaks to the same purpose of such persons (Jas 3:14) If ye have bitter envying and strife in your hearts, glory not and lie not against the truth; this wisdom descendeth not from above. Bitter zeal and strife is an evil token, and a bitter conscience is readily no good conscience. When a man supposing himself to be in the right, is carried on with a spirit of bitterness ... it flows from pride in such persons, exalting themselves above all others. Therefore, as soon as they are deluded and go wrong, they must have a church by themselves, and will join with no other persons in Christian communion, but such as are of their mistaken opinion.
James Durham, Heaven upon Earth, 22 sermons on the joys of a good conscience (1685; Naphtali Press)