In De Trinitate, Hilary writes: Jesus “has commanded us to baptize in the name of the Father and of the Son and of the Holy Spirit (cf. Mt 28:19), that is, in the confession of the Author, of the Only-Begotten One and of the Gift.
The Author of all things is one alone, for one alone is God the Father, from whom all things proceed. And one alone is Our Lord Jesus Christ, through whom all things exist (cf. 1 Cor 8:6), and one alone is the Spirit (cf. Eph 4:4), a gift in all….
In nothing can be found to be lacking so great a fullness, in which the immensity in the Eternal One, the revelation in the Image, joy in the Gift, converge in the Father, in the Son and in the Holy Spirit”.
God the Father, being wholly love, is able to communicate his divinity to his Son in its fullness. I find particularly beautiful the following formula of St Hilary:
“God knows not how to be anything other than love, he knows not how to be anyone other than the Father. Those who love are not envious and the one who is the Father is so in his totality. This name admits no compromise, as if God were father in some aspects and not in others”.
For this reason the Son is fully God without any gaps or diminishment. “The One who comes from the perfect is perfect because he has all, he has given all” (ibid., 2, 8).
Humanity finds salvation in Christ alone, Son of God and Son of man. In assuming our human nature, he has united himself with every man, “he has become the flesh of us all”; “he took on himself the nature of all flesh and through it became true life, he has in himself the root of every vine shoot”.
For this very reason the way to Christ is open to all – because he has drawn all into his being as a man – even if personal conversion is always required:
“Through the relationship with his flesh, access to Christ is open to all, on condition that they divest themselves of their former self (cf. Eph 4: 22), nailing it to the Cross (cf. Col 2: 14); provided we give up our former way of life and convert in order to be buried with him in his baptism, in view of life (cf. Col 1: 12; Rom 6: 4)”.
Fidelity to God is a gift of his grace. Therefore, St Hilary asks, at the end of his Treatise on the Trinity, to be able to remain ever faithful to the baptismal faith. It is a feature of this book: reflection is transformed into prayer and prayer returns to reflection. The whole book is a dialogue with God.
Benedict XVI (b. 1927): St Hilary of Poitiers (General Audience, 10th October 2007.