“IN my opinion He is called Son because He is identical with the Father in Essence; and not only for this reason, but also because He is of Him. And He is called Only-begotten, not because He is the only Son and of the Father alone, and only a Son; but also because the manner of His Sonship is peculiar to Himself and not shared by bodies. And He is called the Word, because He is related to the Father as Word to Mind; not only on account of His passionless Generation, but also because of the Union, and of His declaratory function.”
~St. Gregory Nazianzen, Orations, 30:20.