19 And now, Almighty God, I first must pray You to forgive my excess of indignation, and permit me to address You; and next to grant me, dust and ashes as I am, yet bound in loyal devotion to Yourself, freedom of utterance in this debate. There was a time when I, poor wretch, was not; before my life and consciousness and personality began to exist. It is to Your mercy that I owe my life; and I doubt not that Thou, in Your goodness, gave me my birth for my good, for Thou, Who hast no need of me, would never have made the beginning of my life the beginning of evil.
And then, when You had breathed into me the breath of life and endowed me with the power of thought, You instructed me in the knowledge of Yourself, by means of the sacred volumes given us through Your servants Moses and the prophets. From them I learned Your revelation, that we must not worship You as a lonely God. For their pages taught me of God, not different from You in nature but One with You in mysterious unity of substance. I learned that You are God in God, by no mingling or confusion but by Your very nature, since the Divinity which is Yourself dwells in Him Who is from You.
But the true doctrine of the perfect birth revealed that Thou, the Indwelt, and Thou, the Indweller, are not One Person, yet that Thou dost dwell in Him Who is from You. And the voices of Evangelists and Apostles repeat the lesson, and the very words which fell from the holy mouth of Your Only-begotten are recorded, telling how Your Son, God the Only-begotten from You the Unbegotten God, was born of the Virgin as man to fulfil the mystery of my salvation; how You dwell in Him, by virtue of His true generation from Yourself, and He in You, because of the nature given in His abiding birth from You.
Source: On the Trinity (New Advent)