Schaff, Philip. History of the Christian Church (The Complete Eight Volumes in One). Amazon Kindle Edition, 2014.
Volume 2, Ante-Nicene Christianity A.D. 100-325, “Chapter 10. Montanism.” Sections 109-111, Loc. 17486-17654.
§ 111. Character and Tenets of Montanism.
Schaff observes first that Montanism subscribed to catholic doctrine in every respect (Schaff 2014, Loc. 17581). The errors are rather an exaggeration of the ideas of Christianity. It is not a form of Gnosticism. Where Gnosticism was focused on a theoretical spirituality, Montanism sought to be very concrete in its approach to the spiritual life. According to Tertullian, the Montanists accepted all of Christian doctrine but sought to find and practice a spirituality which would advance beyond the practices of the New Testament (Schaff 2014, Loc. 17593).
Eventually the doctrines did prove heretical as the Montanists required particular gifts of the Holy Spirit to continue unabated. They therefore began to require the Holy Spirit to give gifts in certain ways, rather than simply allowing and welcoming gifts (Schaff 2014, Loc. 17603). The gifts and prophecies had a strong tendency to require further fasting and other ascetic practices. The Montanists then asserted a universal priesthood, including all males and females. This departed from the clericalism which had its roots in the elders of the apostolic period (Schaff 2014, Loc. 17614). The Montanists further pursued a very robust Millenarian point of view. While the idea of a literal minnellium was not unaccepted, the Montanists tended to center their doctrine around these views (Schaff 2014, Loc. 17625). The Montanists were also characterized by extremely severe asceticism and church discipline. At the same time there was a general view that in the broader church the role of discipline was decreasing (Schaff 2014, Loc. 17636). Schaff does find that the zealous ascetic and millennial tendencies can be found in several other, more recent, movements within Christianity (Schaff 2014, Loc. 17652).