For God is in all things by His essence, power and presence, according to His one common mode, as the cause existing in the effects which participate in His goodness. Above and beyond this common mode, however, there is one special mode belonging to the rational nature wherein God is said to be present as the object known is in the knower, and the beloved in the lover. And since the rational creature by its operation of knowledge and love attains to God Himself, according to this special mode God is said not only to exist in the rational creature but also to dwell therein as in His own temple. So no other effect can be put down as the reason why the divine person is in the rational creature in a new mode, except sanctifying grace. Hence, the divine person is sent, and proceeds temporally only according to sanctifying grace.
Again, we are said to possess only what we can freely use or enjoy: and to have the power of enjoying the divine person can only be according to sanctifying grace. And yet the Holy Ghost is possessed by man, and dwells within him, in the very gift itself of sanctifying grace. Hence the Holy Ghost Himself is given and sent.
Reply Obj. 1: By the gift of sanctifying grace the rational creature is perfected so that it can freely use not only the created gift itself, but enjoy also the divine person Himself; and so the invisible mission takes place according to the gift of sanctifying grace; and yet the divine person Himself is given.
Reply Obj. 2: Sanctifying grace disposes the soul to possess the divine person; and this is signified when it is said that the Holy Ghost is given according to the gift of grace. Nevertheless the gift itself of grace is from the Holy Ghost; which is meant by the words, "the charity of God is poured forth in our hearts by the Holy Ghost."
Reply Obj. 3: Although the Son can be known by us according to other effects, yet neither does He dwell in us, nor is He possessed by us according to those effects.
Reply Obj. 4: The working of miracles manifests sanctifying grace as also does the gift of prophecy and any other gratuitous graces. Hence gratuitous grace is called the "manifestation of the Spirit" (1 Cor. 12:7). So the Holy Ghost is said to be given to the apostles for the working of miracles, because sanctifying grace was given to them with the outward sign. Were the sign only of sanctifying grace given to them without the grace itself, it would not be simply said that the Holy Ghost was given, except with some qualifying term; just as we read of certain ones receiving the gift of the spirit of prophecy, or of miracles, as having from the Holy Ghost the power of prophesying or of working miracles. _______________________
FOURTH ARTICLE [I, Q. 43, Art. 4]
Whether the Father Can Be Fittingly Sent?
Objection 1: It would seem that it is fitting also that the Father should be sent. For being sent means that the divine person is given. But the Father gives Himself since He can only be possessed by His giving Himself. Therefore it can be said that the Father sends Himself.
Obj. 2: Further, the divine person is sent according to the indwelling of grace. But by grace the whole Trinity dwells in us according to John 14:23: "We will come to him and make Our abode with him." Therefore each one of the divine persons is sent.