Montanism is named after its founder, Montanus. He had been a pagan priest until his conversion to Christianity in A.D. 155. Montanus claimed that when he fell into a trance, the Holy Spirit spoke directly through him. Later, two women also began to prophesy along with Montanus-- Priscilla and Maximilla. The problem was not that they prophesied; this was certainly nothing new. The difficulty was with the substance of the prophecy-- the claim that the new age had begun with their movement. Montanus acknowledged that a new age began with Jesus, but a newer one began with him. This new age was to be characterized by a rigorous moral life.
The church opposed Montanist doctrine precisely because it diminished the church's understanding of Jesus' work. The new age had begun in Jesus in his crucifixion and resurrection. This new age will be consummated at Christ's return. There was to be no newer age in between. Montanus' claims, therefore, were false.
The Montanists sought to return to what they considered an earlier understanding of the church. They opposed ecclesial formalism and hierarchical organization. They insisted that they church leadership lean upon the Holy Spirit for guidance. Montanus himself claimed that he was the advocate through whom the Holy Spirit spoke, just as he did through the apostles. Montanus claimed that Christ would soon establish his kingdom, and that he (Montanus) would hold a prominent place in that kingdom. In preparation for that kingdom, the Montanists practiced strict asceticism.
The Montanists claimed that their revelation from the Holy Spirit could supercede the authority of Jesus or Paul. One of the chief criticisms of the Montanists was that they were too innovative.