Summary: Sometimes you might have to appear harsh.
2 Cor 6:14-18
14 Be ye not unequally yoked together with unbelievers: for what fellowship hath righteousness with unrighteousness? and what communion hath light with darkness?
15 And what concord hath Christ with Belial? or what part hath he that believeth with an infidel?
16 And what agreement hath the temple of God with idols? for ye are the temple of the living God; as God hath said, I will dwell in them, and walk in them; and I will be their God, and they shall be my people.
17 Wherefore come out from among them, and be ye separate, saith the Lord, and touch not the unclean thing; and I will receive you,
18 And will be a Father unto you, and ye shall be my sons and daughters, saith the Lord Almighty. KJV
Separation is a dirty word even among many Baptists. It is also hard to determine where to draw lines from time to time, but lines must be drawn. I have done a sermon on drawing lines and little boxes. It is tough for some of us to not glad hand and accept as brethren everyone who calls themselves a Christian. Few of us are normally into excluding people. I am a joiner and love friends. I wish that every group that claims to be under Christ's umbrella was truly there, but sadly it is not so.
That makes life tricky as discerning between upfront unbelievers and tares is tough. The upfront are easy because they tell you they want nothing to do with Christ or are not sure or whatever. The tares are tough as it is reasonable to assume that there are some in every church. They look good and talk the talk. In that case, we have to ask God for discernment and love them and hope that through that love and the preaching they hear that at some point they will become real wheat. It has happened often that someone was a pastor, deacon, teacher or musician get saved having been in their capacity for many years.
In Church, we have to allow the Spirit to discern and work with the person as we cannot see the soul. Later, I will speak to brethren who are less than well-behaved. Outside of our local Church, we have to look not only at lifestyle because many cults lead a clean lifestyle and from the outside look like people we can fellowship with as brethren. We have to go past the appearance and judge righteous judgment as Christ enjoined us in John's epistle.
Doctrine, doctrine, doctrine is very important. We can tolerate doctrinal differences in the culture as we live in a free society. Yet, as seekers of the truth we need to split hairs from time to time or at least splitting hairs in the view of other people. While we can tolerate many things we have to take care that our tolerance is not misunderstood as condoning the teaching.
We often hear that as long as it is not a salvation issue or as some say a non-essential doctrine we are told we should just love and seek unity. Frankly, I do not see that in Scripture. Hymaneaus and Philetus were only off kilter in one doctrine; the timing of the resurrection of the dead. It was a big deal and may have been a secondary issue caused by their blasphemy or the primary cause of it, but either way Paul turned them over to satan to be buffeted and if they did not repent to be killed by the devil, like he did the couple living in the sin of incest in Corinth.