The Angelic Doctor Against the Errors of the Greeks - Part Two - Chapter 19

That the Holy Spirit is spirated from the essence of the Son.

Also confirmatory of this is the fact that in the same texts it is stated that the Holy Spirit is spirated from the essence of the Son. For Athanasius says in his discourse on the Council of Nicaea: “We adore the Breath of life from the essence of the Son, the Spirit, the coeternally spirated God.”  And again in the same work: “From his essence God spirated the Holy Spirit.”  And in his letter to Serapion: “The heretics are disinherited by the Son because they do not accept the Holy Spirit as in essence God spirated from his essence.”  And in the same letter explaining as it were what “from his essence” means, that is, “from himself as essence”, he says as follows: “The Son born of the Father, truly possessing in himself the Father’s nature, retained not the property of paternity, but that of natural communicability, so that of himself from himself as his own essence he should spirate not a son by generation, but the Spirit, equal and coeternal with him as God in all things.”  And the same point it repeatedly made in his texts.

From this it is clear that when it is asserted that the Holy Spirit is spirated by the Son, this cannot be said in reference only to his temporal procession, but to his eternal as well whereby the Holy Spirit receives the divine essence from the Son.