A heresy is an obstinate denial by a baptized person of some truth of the Christian faith. It's an exaltation of one part of the Truth to the exclusion of the rest. A Trinitarian heresy is an attack on the Blessed Trinity. Part of the Church job is to protect itself against heresies of these sorts. This is where the Church doctrine comes in. From what I have learned from a fantastic teacher a couple of months ago is that the Church is like a "Pearl." The Oyster is the Church. It's just there and well established if I may add. A heresy is like a grain if sand. It can easily irritate the oyster. In the inside if that oyster is the "pearl." The pearl represents the Church Doctrine. The Doctrine helps heresies not exclude other details that makes their reasons faulty. The Church teachings about The Trinity is found in Scripture,developed over time, and is also a response to heresies. At this point your probably wondering "Isis...why is it important for the Church to battle such heresies?" My response is this... " Understanding Who Jesus is reveals God to us..." The Trinity is hinted many times within the Old Testament. Look at Genesis 1:26-27...this is the only time in the Bible God speaks of Himself in the plural, and when Abraham was greeted by 3 MEN. The most popular Trinitarian heresies are Gnosticism,Marcionism, Montanism, and Manichaeism. The first heresy to be spoken about today is Gnosticism. Gnosticism was founded by Simon Magus. They teach that the material world should be shunned and spiritual world should be embraced, that Jesus was merely human and later on attained divinity through gnosis and taught His disciples to do the same. The Church response was that The physical world is good. God even says so in Genesis, humans are physical and spiritual beings and both are good, salvation comes fom grace, not merit, and God wants all to be saved. Marcionism was create by Marcion. Marcionism believed that Jesus was sent from God, and Paul Tarsus was his chief apostle, but rejected the Hebrew Bible and The God Of Israel, and taught that Hebrew God was a separate and entity than the "all-forgiving" God of the New Testament. The response was that He was no different. He is all forgiving and loves us all. Montanism was found by Montanus. He taught that the New Jerusalem was suppose to appear on a mountain, taught that He and his followers were "enlightened" and chosen by the Holy Spirit to be prophets, His apostles could forgive sins, they recognized women as bishops, have women covered and forced to wear veils, didn't allow remarriage after divorced or after being widowed, paid people who preached Montanus Doctrine. St. Jerome responded to this heresy by stating "Ignorance of Scripture is Ignorance of Christ." Last, but not least. Manichaeism. This heresy was founded by a man named Mani. He taught that Satan created this world an made it corrupt evacuee God took no time in the formation of creation, that light and darkeness plays an influence in people souls, this world consists of battles between God and Satan. We as the Church respond that God created this world, and we rule it with free will. God also has zero flaws when it comes to creation because He made it in His eyes, His definition of perfection, and it took 6dys and a Sabbath to have this magnificent world created for you and me. All these heresies sound unbelievable, but this is what some people thought. Heresies believe it or not are actually good for the Church because it helps us reaffirm out beliefs an help people u d'état and why it is not right, and correct this minor error, and also helps the Church not to have this problem again in the near future. In conclusion of this The Trinity is a "first-rate mystery" as St. Augustine once said. Keep the faith and have a blessed week.
Anyone who DENIES the Trinity is in danger of LOSING THEIR SALVATION, and anyone who TRIES to UNDERSTAND it is in danger of LOSING THEIR MIND.
-St. Augustine of Hippo
In no other subject is error more dangerous, inquiry more difficult, or discovery more rewarding...
-St. Augustine of Hippo
Truth is the Trinity...
-Bertrand de Margerie S.J
The Blessed Trinity is the mystery of mysteries, before which even the seraphim veil their countenances singing with astonished wonder their trice repeated "Holy."
-Matthias Joseph Scheeben