Monarchianism is a doctrine that emphasizes God as one indivisible being,[1][2][3][4] in direct contrast to Trinitarianism, which defines the Godhead as three co-eternal, consubstantial, co-immanent, and equally divine hypostases.
During the patristic period, Christian theologians attempted to clarify the relationship between the Father, Son and Holy Spirit.
It holds that the Son was not co-eternal with the Father and that Jesus Christ was essentially granted godhood (adopted) for the plans of God and for his own perfect life and works.
[3] Modalistic monarchianism (or Modalism) considers God to be one, who appears and works through the different "modes" of Father, Son, and Holy Spirit.
Notable adherents included Noetus, Praxeas, and Sabellius, hence why the view is commonly called Sabellianism.