Taylor Marshall gives us a checklist of heresies. See how many of them you recognize today.
Docetism teaches that Jesus only appeared to be human as a phantom. On the contrary, the Catholic Church teaches that Christ if fully God and fully human.Arianism teaches that Jesus not fully God, but only like God in a subordinate way. On the contrary, the Catholic Church teaches that Christ if fully God and fully man.
Nestorianism teaches that Jesus is two “persons” - Jesus the human son of Mary and Jesus the divine Son of God. On the contrary, the Catholic Church teaches that Christ is one person with two natures: divine nature and human nature.
Monophysitism teaches that Jesus is fully God but not fully man, the humanity of Christ being swallowed up by His divinity. On the contrary, the Catholic Church teaches that Christ has two natures: divine nature and human nature.
Monothelitism teaches that Jesus has only one divine will. The Catholic Church teaches that Christ has two wills: a divine will and a human will belonging to His human soul.
Iconoclasm teaches that images are idolatrous. On the contrary, the Catholic Church defends the use of Christian (not pagan) images since Christ became visible through the incarnation.
Pelagianism denies original sin and teaches that grace is not necessary for salvation. On the contrary, the Catholic Church teaches that we are born in original sin and saved by grace through faith and works.
There are no new heresies. There are only old ones dressed up in new forms. Sometimes they combine to attack God from a number of angles, but they can usually be broken down into their component parts.
If there's one missing from the list, it's Gnosticism. Gnosticism does not believe that the world is inherently good; it believes that matter is the creation of a fallen being known as the Demiurge, and that we are chained to matter. We are only freed because of illumination, or wisdom, sent by the benevolent creator God to free us from this world. Usually Gnosticism allies with Pelagianism and Docetism.
Gnosticism is supposedly the latest rage again, but I doubt very few admirers of The Da Vinci Code who think of themselves as Gnostics really understand its implications. I had a friend praise Gnosticism to me and I simply replied, "Yes, matter really is evil, isn't it. Curse our evil human bodies."
Naturally, this answer surprises so-called modern Gnostics, who don't understand anything about true, historical Gnosticism. In reality, modern Gnostics are a form of Pelagians, who believe in the perfectability of man without any sort of divine intervention, or Arians, who simply want to deny the divinity of Christ. Probe what they believe, and you'll usually find that their philosophy consists of the premise that any cudgel is good enough, provided it is used to strike Mother Church.