Since there is only one form of Godhead in the indivisible unity of His self-revelation as Father, Son, and Holy Spirit, we believe that He is eternally triune in Himself. It is, indeed, through the Trinity that we believe in the unity of God, but it is also through acknowledgement of the oneness and identity of being in the Son and the Spirit with the Father that faith in the holy Trinity takes its perfect and full form. This is the doctrine of God as Trinity in unity and unity in Trinity. It is hardly surprising, therefore, that Athanasius should equate theologia, in its deepest sense as the knowledge and worship of God as He is known both through Jesus Christ and in the Holy Spirit and as He is eternally in Himself, with the doctrine of the holy Trinity.
From: Trinitarian Perspectives: Toward Doctrinal Agreement by Thomas F. Torrance (Edinburgh: T&T Clark, 1994), pp. 7-8.