What is the church according to the one who sees all, knows all, and judges in complete, inexorable justice and righteousness?
“This is what the Son of God says, the one who has his eyes like a fiery flame and his feet like fine bronze: ‘I know your works, and your love, and faith, and service, and patient endurance—and your last works are greater than the first. But
I have against you that you tolerate the woman Jezebel, the one who
calls herself a prophetess, and teaches and deceives my slaves to commit
sexual immorality and to eat food sacrificed to idols. And I have given her time in order to repent, and she did not want to repent from her sexual immorality. Behold,
I am throwing her into a sickbed and those who committed adultery with
her into great affliction, unless they repent from her deeds. And
I will kill her children with deadly disease, and all the churches will
know that I am the one who searches minds and hearts, and I will give
to each one of you according to your deeds. But I say to you, to the rest who are in Thyatira, all those who do not hold this teaching, who have not known the deep things of Satan, as they say, I do not put upon you any other burden. Nevertheless, hold fast to what you have until I come. And the one who conquers and who keeps my works until the end, I will give him authority over the nations, and “he will shepherd them with an iron rod; he will break them in pieces like jars made of clay,” as I also have received from my Father, and I will give him the morning star. The one who has an ear, let him hear what the Spirit says to the churches.’
The church is not without false teachers. The tree shall be known by its fruit. Which is why we all have a duty to know God's Word, so we may accurately discern what is right teaching from what is wrong.
"Dear friends, do not believe every spirit, but test the spirits to determine if they are from God, because many false prophets have gone out into the world. By this you know the Spirit of God: every spirit that confesses Jesus Christ has come in the flesh is from God, and every spirit that does not confess Jesus is not from God, and this is the spirit of the antichrist, of which you have heard that it is coming, and now it is already in the world.
You are from God, little children, and have conquered them, because the one who is in you is greater than the one who is in the world. They are from the world; therefore they speak from the world and the world listens to them. We
are from God. The one who knows God listens to us; whoever is not from
God does not listen to us. By this we know the Spirit of truth and the
spirit of deceit." 1 John 4