In his own time, Teilhard de Chardin was condemned as a heretic, and now there are dorms named after him at Catholic colleges. Let's also not forget that Jesus himself was condemned as a heretic.
Not everyone who tries to make a big difference (and be called a heretic as a result) is of God's.
The most radical ones are possibly the only ones capable of deceiving the elect, saints, prophets, etc. These are the toughest false teachers to crack since they're teaching very close to the truth. It's harder to spot the lies they are teaching.
And often these persons can even let themselves undergo extreme hardships even martyrdom making their followers blind to their teachings (who assume everything they say is truth - after all, martyrs can't be wrong!!)
I think everyone has an idea or two about 'secret agents' in films, TV series. They can be quite fearless for their cause, even brave death and torture itself. They are often employed in deceiving the enemy and that they can execute even against the most intelligent and smartest of persons.
Some false teachers are like the secular 'double agents'. They can let themselves suffer real persecution, torture, even martyrdom under the label of Christianity just so they can inject some lies into the truth.
If false teachers came with long beards and wielding automatic rifles, you'll most likely avoid them! If false teachers came via expensive, white suits, off their private jets, they may attract many, but not the elect - the real Christians... If false teachers came wearing tattered clothes, bloodied, and limping, they might actually deceive even the saints! Even if they speak some lies.
Our spiritual enemies are certainly NOT dumber than the CIA, nor the KGB, etc. In fact, the vast disciplines of infiltration, stealth, and deception these agencies employ may have ultimately come from our spiritual enemies. And the bad news is, we are their enemy and we are in the middle of this battle! There is only one small escape, and simple-mindedness is not an option!
