There is mention in the Bible (NT) of heresies going around in the churches of the 1st century. Heresies have always invaded the church. Why do you think it is different now or for the last 15 centuries?
A
heretic is one who knows and has been taught and understands the apostolic faith, and believes in a teaching that is contrary to the faith which is a heresy.
Heretics and apostates have come in the Catholic church since apostolic times. Those who have not been correctly catechized in the faith, and by no fault of their own believe in a faith that is contrary to the apostolic faith cannot be labeled a heretic. Although the contrary belief’s to the Apostolic Catholic faith are labeled heresy as a warning for the believers, so as “not to be moved by every wind of doctrine” that has come for the past 1500 years.
Paul and others label heretics because they have been taught the “Truth” but believe contrary. Paul’s epistles gives warning of these that have entered the Church and will enter the church. Those of pagan belief’s are not heretics, but the lost, you have to Know of the Truth and believe contrary to the Truth to be labeled a heretic.
The bible never teaches heresies, The bible is the Word of God, and God breathed.
Truthfully the heresies are not different or new, they just repeat themselves in different ages and come in different disguises that the serpent uses to deceive the sheep of God and twist the Truth of God. We have the promise of Jesus Christ that his “True” presence will be with his church always, to protect his teachings “infallibly”.