Montanism is named after a self-styled prophet named Montanus who lived in Asia Minor in the second century AD. Montanism, also called the Cataphrygian heresy or New Prophecy, taught that the Holy Spirit was continuing to give new revelation through Montanus and his followers and that Jesus would soon bring the New Jerusalem to a place in Phrygia.
He and his two prophetesses Priscilla and Maximilla, known as "the Three," prophesied in a frenzy with convulsions in a way that was "contrary to that which was the custom from the beginning of the church," according to Eusebius in Ecclesiastical History 5.16.1. Montanus claimed to be the embodiment of truth, though, speaking equal to Scripture. Tertullian also wrote about him in De Fuga in Persecutione , 9. His followers claimed to be "spirit-filled" and to possess a more advanced form of Christianity. Since New Jerusalem was soon descending upon Phrygia, many migrated to that area.
The church rejected Montanus in AD 177 because a two-tiered Christianity of those with Spirit and those without was unbiblical and they expected New Testament prophets to follow the pattern of earlier prophets of God - rational, understandable, in control, and always speaking with reason and understanding. Tertullian defended the movement and became a leader of the Montanists in Carthage. Also, Montanus claimed to be the Father, the Word, and the Paraclete.
(Sounds like a modern cult to me! Nothing new under the sun. Are the charismatic leader, centralized location, doomsday message, "advanced form of Christianity," and difficult-to-understand message (literal babbling and convulsing) as old as Christianity? If that's true, it's concerning Tertullian accepted them. But then again, how much do we really know about anything from that long ago?)
(https://www.gotquestions.org/montanism.html, accessed 5/28/2023)
The heretical movement of Montanus was an impetus toward the recognition of a closed canon of the written Word of God. He taught that the prophetic gift was never withdrawn, so he could add to the Word of God. The pressure to deal with him intensified the search for a basic authority, and apostolic authorship or approval became recognized as the only sure standard for identifying God's revelation. Even within Scripture, 1st century prophets were subordinate and subject to apostolic authority (1 Corinthians 14:29-30; Ephesians 4:11).
(The Origin of the Bible: Newly Updated by F. F. Bruce, J. I. Packer, Philip W. Comfort, and Carl F. H. Henry, 2020. The Canon of the New Testament by Milton C. Fisher, Pages 75.)
New Testament Etymology
The first appearance of the term "New Testament" was in a composition against Montanism by an unknown author in circa A.D. 190.
(The Origin of the Bible: Newly Updated by F. F. Bruce, J. I. Packer, Philip W. Comfort, and Carl F. H. Henry, 2020. Biblical Languages by Larry Walker. Section One: The Authority and Inspiration of the Bible. Page 66)