Scripture sets forth a distinction of the Father from the Word, and of the Word from the Spirit. Yet the greatness of the mystery warns us how much reverence and sobriety we ought to use in investigating this. And that passage in Gregory of Nazianzus vastly delights me:
“I cannot think on the one without quickly being encircled by the splendor of the three; nor can I discern the three without being straightway carried back to the one.” Let us not, then, be led to imagine a trinity of persons that keeps our thoughts distracted and does not at once lead them back to that unity. Indeed, the words “Father,” “Son,” and “Spirit” imply a real distinction—let no one think that these titles, whereby God is variously designated from his works, are empty—but a distinction, not a division.
Institutes of the Christian Religion, Volumes 1 & 2, ed. John T. McNeill, trans. Ford Lewis Battles, The Library of Christian Classics (Louisville, KY: Westminster John Knox Press, 2011) Vol. 1.8.17. p. 141-142.