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I was having a discussion with an Anglican underneath one of my posts. I’m sure he is sincere and well-meaning and all that (most people are), but be that as it may, he started objecting to how the Catholic Church has doctrinal requirements in order to be a member. This is what gives many people pause. But it’s a thoroughly biblical idea. This is what creeds and confessions deal with. There is such a thing as true doctrine and it is one unified doctrine.
My Anglican friend didn’t seem to grasp this. He wrote things like the following (I quote):
. . . it is entirely unnecessary for us to worship together in unity that we should be in wholesale agreement with each other over exactly how many angels can indeed dance on the head of a pin (or indeed anything else).
No-one has the “final say” as to what Scripture teaches: that’s the whole point.
Why should theological orthodoxy (or lip service acquiescence) be a necessary condition for membership of the church?
. . . why do you also require that I submit to theological orthodoxy and deny my own conscience as a criterion for acceptance into the Catholic Church?
. . . [God] didn’t give us any really new commandments, particularly not “throw out anyone who won’t believe all the same things as you” or “if you get the doctrine of the trinity wrong you will go to hell”.
[Jesus] didn’t say “purge the heretics” though.
This last statement led me to make the following reply:
You don’t seem to have read the New Testament very much; or if so, you must have missed the many passages about false teachers and heresy.
There are all sorts of passages about those who pervert the true faith, and ultimately to separate from them if they do so. I don’t think they apply so much to Protestants, but to those who deny the Trinity, etc.
2 Corinthians 11:12-15 (RSV) And what I do I will continue to do, in order to undermine the claim of those who would like to claim that in their boasted mission they work on the same terms as we do.  For such men are false apostles, deceitful workmen, disguising themselves as apostles of Christ.  And no wonder, for even Satan disguises himself as an angel of light.  So it is not strange if his servants also disguise themselves as servants of righteousness. Their end will correspond to their deeds.
Galatians 2:4-5 But because of false brethren secretly brought in, who slipped in to spy out our freedom which we have in Christ Jesus, that they might bring us into bondage —  to them we did not yield submission even for a moment, that the truth of the gospel might be preserved for you.2 Peter 2:1 But false prophets also arose among the people, just as there will be false teachers among you, who will secretly bring in destructive heresies, even denying the Master who bought them, bringing upon themselves swift destruction.
1 John 4:1 Beloved, do not believe every spirit, but test the spirits to see whether they are of God; for many false prophets have gone out into the world.
Revelation 2:2 I know your works, your toil and your patient endurance, and how you cannot bear evil men but have tested those who call themselves apostles but are not, and found them to be false;
Then there are a host of verses about truth, “the truth” etc.:
Romans 2:8 but for those who are factious and do not obey the truth, but obey wickedness, there will be wrath and fury.
2 Corinthians 11:10 As the truth of Christ is in me, this boast of mine shall not be silenced in the regions of Acha’ia.
2 Corinthians 13:8 For we cannot do anything against the truth, but only for the truth.
Galatians 5:7 You were running well; who hindered you from obeying the truth?
Ephesians 4:25 Therefore, putting away falsehood, let every one speak the truth with his neighbor, for we are members one of another.
Colossians 1:5 . . . Of this you have heard before in the word of the truth, the gospel
2 Thessalonians 2:10 and with all wicked deception for those who are to perish, because they refused to love the truth and so be saved.
1 Timothy 3:15 the household of God, which is the church of the living God, the pillar and bulwark of the truth.
2 Timothy 1:14 guard the truth that has been entrusted to you by the Holy Spirit who dwells within us.
2 Timothy 3:8 As Jannes and Jambres opposed Moses, so these men also oppose the truth, men of corrupt mind and counterfeit faith;
Then there are passages about “the faith”: which presupposes that it is one body of doctrine, or orthodox teaching; not a potpourri of all sorts of contradictory doctrines: