Chapter 46 — That Christ was conceived by the Holy Spirit

Although every divine work that has its effect among creatures is common to all the Trinity, as we have shown above, (Bk. 4, ch. 21.) the fashioning of Christ’s body by divine power, although common to the three persons, is fittingly ascribed to the Holy Spirit.

This seems becoming to the Incarnation of the Word. For just as our word, which is conceived in our mind, is invisible but becomes perceptible to the senses when it is spoken, so the Word of God is invisible as regards his eternal generation in the bosom of the Father, but became visible to us through the Incarnation. Therefore, the Incarnation of God’s Word is like the vocal utterance of our word. Now we give expression to our word through the breath (per spiritum) by which we form words expressive of our thoughts. It is therefore fitting that the flesh of the Son of God should be formed by his Spirit.

This is also in keeping with human generation. For the active power of human seed is actuated by the spirit in drawing to itself the material provided by the mother; the same power being derived from the spirit whose purity accounts for the whiteness of the foam-like semen. Accordingly, when the Word of God took to himself a body from a virgin, it was fitting that this body should be fashioned by the Holy Spirit.

This was also fitting as indicating the motive of the Incarnation of God’s Word. For this motive could be no other but God’s love for man whose nature he wished to unite to himself in unity of person. Now, in God, it is the Holy Spirit who proceeds as love, as proved above. (Ch. 19.) Therefore, the work of the Incarnation is fittingly ascribed to the Holy Spirit.

Moreover, Sacred Scripture is accustomed to ascribe all graces to the Holy Spirit, because that which is freely given would seem to be bestowed through the love of the giver. Now no grace has been bestowed on man greater than his union with the divine person. Therefore, this work is fittingly ascribed to the Holy Spirit.