Actually, that is not true, we all do not know that. You like to make unsupportable statements it seems.
Revelation 2:2
“‘I know your works, your toil and your patient endurance, and how you cannot bear with those who are evil, but have tested those who call themselves apostles and are not, and found them to be false.
Matthew 7:15
“Beware of false prophets, who come to you in sheep’s clothing but inwardly are ravenous wolves.
1 Corinthians 11:19
for there must be factions among you in order that those who are genuine among you may be recognized.
2 Corinthians 11:13
For such men are false apostles, deceitful workmen, disguising themselves as apostles of Christ.
Acts 20:30
and from among your own selves will arise men speaking twisted things, to draw away the disciples after them.
1 Timothy 4:1
Now the Spirit expressly says that in later times some will depart from the faith by devoting themselves to deceitful spirits and teachings of demons
1 John 2:19
They went out from us, but they were not of us; for if they had been of us, they would have continued with us. But they went out, that it might become plain that they all are not of us.
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
Matthew 24:24
For false christs and false prophets will arise and perform great signs and wonders, so as to lead astray, if possible, even the elect.
Jeremiah 23:32
Behold, I am against those who prophesy lying dreams, declares the LORD, and who tell them and lead my people astray by their lies and their recklessness, when I did not send them or charge them. So they do not profit this people at all, declares the LORD