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 12. The Development of Catholic Theology in Conflict with Heresy” Sections 137-158, Loc. 18758-20235.
§ 152. Sabellianism.
Schaff describes Sabellius as “by far the most original, profound, and ingenious of the ante-Nicene Unitarians, and his system the most plausible rival of orthodox trinitarianism” (Schaff 2014, Loc. 19761). Sabellius had a significant influence in Rome as well as in the Pentapolis (Egypt). He was excommunicated by Dionysius of Alexandria in 260 or 261, starting a hot theological debate. Sabellius affirms the Holy Spirit, as opposed to many Monarchians, who concentrated on the Father and the Son (Schaff 2014, Loc. 19768). However, the trinity as Sabellius sees it is still modalistic. The persons of the Trinity are successive revelations of a unified God who lacks the threefold distinctive persons. The different revelations of God have different functions in the world. They do not act at the same time, because only one can exist at a time (Schaff 2014, Loc. 19776). Athanasius considered this a Stoic philosophy. Schaff relates it to Pythagorean philosophy as well (Schaff 2014, Loc. 19784).