Inconsistent, unscriptural behavior is subject to reproof and if not corrected, the believer is to withdraw or separate himself from those who refuse to be corrected. Disobedient believers are to be avoided. And if any man obey not our word by this epistle, note that man, and have no company with him, that he may be ashamed. Disobedience here includes both doctrinal and practical matters. Divisive brethren are to be avoided.
Erroneous doctrine is divisive.
Avoid those whose erroneous teachings cause divisions. Since the Scripture does teach that one should separate from unbelievers, then those who do not do so are disobedient to that teaching, and they should be avoided . It means that the Biblical church will not be a part of any association or ecumenical campaign which includes cooperation with liberals. Does not this mean that a local church should not fellowship with other evangelical churches which cooperate with liberals. True reverence for God's word is expressed by obedience to it.