"Shake off the dust of your feet" (Matt. 10.14) from mistaken beliefs - An action to indicate that they will have nothing to do with whatever place where Christ is rejected.
Various Types of Errors Inside Christendom
Each of the church periods foretold in Revelation 2 & 3 were given to warn the church not to make these mistakes through the past 20 centuries. The first three church periods were consecutive, which gave way to the next. But the last four church periods remain with us in full force today.
2. Pentecostals - false tongues of Montanism, a 2nd Century heresy: an unholy response to the Smyrna church period in the second century.
3. Eastern Orthodox - Constantine "high tower," married to the world: Pergamum church period in the third century and the beginning of denominations and national churches. National churches (e.g. Anglican, Russian Orthodox, etc.) exceed the boundary of Biblical locality.
4. RCC (Rev. 14.8,
ch.17) - great harlot of
religious Rome: the fourth century, Thyatira
church period, with various many false teachings
such as have their goddess in calling Mary
6. Brethren movement in the
19th century - these ones were the
Philadelphia church period. God asked that
they not lose what they had. When one is
objectively accurate, there is the risk of
losing that subjective relationship with Chirst.
Various Types of Errors Outside Christendom
Too many to mention
Mormons (God is gods); Christadelphians and JW's (deny the Trinity and Jesus Christ as the 2nd Person of the Godhead); non-OSASers (no faith in OSAS); open theism (God doesn't have foreknowledge). There are actually over 40,000 adherents in the world today.
Other Important Differences
Though some persons may be saved in the above man-made organizations that is the exception not the rule, since God does not employ denominations. Also undesirable doctrinally, are historicalists (ammill. post-mill., preterism), antinomianism (accepting substitution without co-death identification), and bipartite fallen man teachings.
Many other things not mentioned, ought to be obvious to Christians.
Warning About Judging
"Ye shall do no unrighteousness in judgment: thou shalt not respect the person of the poor, nor honor the person of the mighty; but in righteousness shalt thou judge thy neighbor" (Lev. 19.15).
If someone tells you that you can not judge ever, they do this in order to try to cause you to go into passivity. Understand what God is saying!
The Word of God clarifies this matter: Matt. 7.1-6; 7.15-23;
1 Cor. 4.3-5; 1 Cor. 5.1,2; John 12.47; Matt. 23.3; 2 Peter 2.21-22; 2 Tim.
4.14, 4.10, 1.15 - judge the forum owners and moderators for their false
teachings (Matt. 7.15) in their unrighteous forums (v.20) - especially by what
they teach which is the "fruit" (v.16) of a false prophet, not just their
Sometimes we have to tell what we have seen. When you are falsely
judged, say as Jesus did, "by whom do your children cast out? therefore they
shall be your judges," (12.27) to mean "they shall judge you for what you
have said since you do the same thing you accuse of".
What a strange accusation to accuse that we can not discern. Praise the Lord we can discern, as well as judge when called upon by God to do so (Ex. 18.13-27). "Judge not" (Matt. 7.1) means not to act like a judge or ruler or critical and hairsplitting, which will cause one to lose the two blessings of not being judged or receiving the rewards of the millennium at judgment seat. Yet, we are not to judge altogether either (Matt. 7.5).
Such hand washing of noble ideals of the dogs and the swine close to the door of the church will not accept God's grace of forgiveness of sins. Instead, these swine, church-goers pretending, are unclean, who do not care for the truth. And the dogs are unregenerates also (Matt. 7.6; Phil. 3.2; Rev. 22.15; cf. 21.8 - dogs are in the lake of fire without the Holy City). So let us not cast pearls (experiences received from God) or give holy things (truths in general from God) to many of these forums or their owners or their moderators who continue to promote false teachings.
Praise the Lord, we may discern and judge in right measure pleasing to God.