Calvin on the Anti-Trinitarian Heresy

Moreover, Satan, in order to tear our faith from its very roots, has always been instigating great battles, partly concerning the divine essence of the Son and the Spirit, partly concerning the distinction of the persons. He has during nearly all ages stirred up ungodly spirits to harry orthodox teachers over this matter and today also is trying to kindle a new fire from the old embers. For these reasons, it is important here to resist the perverse ravings of certain persons.