Holiness is both a negative and positive principle in relation to the Body of Christ. There is no true unity, biblical unity, that does not have truth as its center and holiness at its gates. Holiness separates and it unites.
Separation
I. From the World
II. From False Teachers and Factitious Men
III. From Disobedient Brethren
Is it not interesting that what those who emphasize unity decry the most–separation– is the very means by which Scripture says unity is to be preserved?
Notice his last statement about separation - those who put a big deal on uniting are the same ones who cry out against those that separate - they are actually crying out against unity! Who wouldn't want to separate? Those that want to remain of the world, under false teachers or those with itching ears (tell me like I want to hear it preacher) and those who willfully are disobedient against God in separating from disobedient brethren and thereby are disobedient themselves. They will mock those that separate as the Bible instructs, yet they are mocking God and despising those that are good.
He states the purpose of separation is purity of the gospel, preservation of unity and protection of saints, preservation of unity among the brethren, protecting the purity of the Body of Christ and that the disobedient brethren may be ashamed and repentant of his sin and return.
This is why those that don't want holiness do all 3 of the things that holiness requires separation from! They UNITE with the world. They UNITE with the false teachers. They UNITE with the disobedient brethren. They do the opposite of what true holiness does and thereby, they reveal they are not of God. So think about that the next time someone you know gets a stink about separation - they are looking to unite back with what they were once separate from! It won't be long they will show their true desires, which is to be unholy.