The definitive affirmation of the orthodox Christian faith in the One and the Three, formulated at the Council of Nicaea in 325, opened with the declaration: “We believe in one God, Father, all-sovereign Maker of all things, both of those that are visible and of those that are invisible” [ … ] That affirmation is still authoritative and binding upon most of Christendom, albeit in the slightly different formulation that was adopted at the First Council of Constantinople in 381: “We believe in one God, Father, all-sovereign Maker of heaven and earth, of all things, both of those that are visible and of those that are invisible” [ … ]
It is essential to recognize both of these statements of trinitarian doctrine opened with an unequivocal confession of the monotheistic faith, in keeping with the dogma of the Trinity was not only compatible with monotheism but essential to it (given the universal Christian practice of treating Christ as divine). No less noteworthy in the creed is their use of cosmology as the point of reference in the trinitarian doctrine. The trinitarian doctrine and the cosmological doctrine of the Cappadocians were based upon Nicaea and then contributed to Constantinople, and each of these two doctrines was used to clarify the other. Trinity and cosmology were therefore intimately related, and in some sense correlative, doctrines.
Jaroslav Pelikan, Christianity and Classical Culture (Yale University Press: 1993) p. 248