Funny you should ask.
I was just re-listening today in the car to a series of lectures on the Early Church heresies by Father Josiah Trenham. He is a great story teller and these heresies come alive. Father Trenham builds up the case for each heresy, before explaining why the Church has to condemn them. In declaring what the Church isn't, heresies helped the Church understand what she is. For example, Gnostics such as Marcion drew up original NT canons before the Orthodox Church did, thereby catalyzing the Church to codify the actual canon. Some of our greatest saints and theologians such as St Irenaeus, St Athanasius and St Augustine arose because of their writings against heresies (Gnosticism, Arianism and Donatism and Pelagianism, respectively).
The lectures cost $10 to buy all 7, but the first one is free so you can try it out.
Here's a description of the course:
"The Doctrines of Demons: A History of Early Heresy
By Fr Josiah
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In this series of 7 lectures, Father Josiah examines the major heresies of the first four centuries of Christian history, explaining the mind of the Church about the errors of each heresy, commenting upon how each heresy survives in some form today, and articulating the true faith in contrast.
The first lecture (available at no charge),
Heresy according to the Scriptures and the Church Fathers, is the introductory lecture in a seven-part lecture series entitled
The Doctrines of Demons: A History of Early Heresies. This initial lecture provides our listeners with a theological overview of the concept of heresy according to the Scriptures and the Holy Fathers of the Church. As the Christian faith is the greatest good on the earth, so heresy is the greatest evil in the world leading to the everlasting ruin of human persons. As the Christian faith enlightens mankind through the preaching of the Gospel, the true faith at the same time exposes error and heresy, castigating it as such in order to protect the faithful from harm and recalling those who have sadly embraced the doctrines of demons. This complimentary gift is available below.
The remaining lectures, 2 through 7 can be purchased for $1.99/each, or all 7 for $14 $10, and are available online as shown below.
All 7 Lectures; was $14, now : $10.00
All 7 Lectures; was $14, now : $10.00
Lecture 1: Heresy according to the Scriptures and the Church Fathers: $0.00
Lecture 2: Early Judaizing and Gnostic Heresies: $1.99
Lecture 3: The Heresy of Arianism: $1.99
Lecture 4: The Heresy of Donatism: $1.99
Lecture 5: The Heresy of Pelagianism: $1.99
Lecture 6: The Heresy of Manicheanism: $1.99
Lecture 7: The Heresy of Jovianism & Heresies concerning Marriage and Virginity: $1.99
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