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.
How many things did Jesus correct in the teachings of the Pharisees and the Sadducees? Some were salvation related in that they were rejecting Christ as Messiah based upon their exegesis or more often eiegesis of the Scriptures. Others like the traditions of washings or how they handled the Sabbath day journey were not directly related to salvation, but they were errors. He corrected them on all points.
The Holy Spirit came to lead us into ALL truth, not just some truths or just the non-essential, but all truth. So, is the mode of baptism a salvation issue? No, a person can be saved by faith in Christ and in their ignorance as a new babe in Christ be led to have a rite called baptism that uses affusion/pouring or aspersion/sprinkling. Did they lose their salvation? No. Were they correctly baptized? No. If they come to our church should we encourage them to baptized by immersion? Definitely.
This where the ecumenical movement becomes a real problem. They hook up with everyone. Amos asks how we can walk together unless we be agreed. You cannot. It only creates confusion and delusion by trying to mix a myriad of doctrines together. Would you admit a person who claims to be a mathematician into your school if he believed that two and two are five or that you can multiply by zero? No, because he is wrong. I cannot be a member of a group of saved people who baptize babies or sprinkle or pour because they are wrong. Can I love them as a person? Yes. I just cannot plow in the same field with them. It may be a sincere belief and error, but error is to be corrected, not overlooked or ignored in the name of anything. Love, grace and truth are a trinity as you cannot truly have any of those if they are not all present. Truth without love or grace is not truth. Love or grace with truth is not love or grace. Thus we must strive to know the truth in all arenas. It is a bit of a tightrope at times, but we need to walk that tightrope well or what we think is a safety net under us will really be a snare.