Father Cassilly writes: “In the consummation of our union with God in heaven, time and space will seem to vanish for us, a moment of this sublimation into companionship with the Deity will lengthen into a century, and a century appear but as a moment. ‘One day in Thy courts is above thousands’ (Ps 83:11). God forever in me and I in Him. This will be our rapturous state in glory; and it has begun already, albeit in an imperfect manner.”
“It is true that the Persons of the Trinity cannot be separated, that by a mutual indwelling, which theologians call ‘circumincession,’ where one is, the others must be. Thus in the Incarnation, though only the Word became flesh, yet the Father and the Spirit were never absent from the Son of man. In this sense Father and Son certainly accompany the Holy Ghost in His mission of sanctification.”
“But, further, it is an axiom in theology that all actions of God in creatures are common to the Three Persons. For, actions proceed from the nature of a being, and the Divine Nature is identical in the Three Persons of the Blessed Trinity. Hence all relations between God and creatures, save that arising from the hypostatic union in Christ, which is terminated in the Person of the Word, are common to all the Persons of the Trinity.”
“The union of God and the soul is not hypostatic, as is that of the Incarnate Word where two natures subsist in one Person. It is but an accidental union, the Holy Spirit and the soul each remaining distinct and retaining its personality. According to this teaching the sanctification of the soul proceeds equally from the Three Divine Persons; and the indwelling of the Deity is alike of Father, Son and Holy Ghost. And this is borne out by the words of Christ: ‘If anyone love Me, he will keep My word, and My Father will love him, and We will come to him, and make Our abode with him’ (Jn 14:23). Here it is promised that the Father and the Son will dwell in the just soul, just as in the passages quoted before this, inhabitation is attributed to the Third Person.”
“This interpretation is contained in the writings of the Fathers. To quote St. Ambrose: ‘As we are the temple of the Father and the Son so also are we of the Holy Spirit, not many temples but one temple, because a temple is of one Power.’ And St. Augustine tells us explicitly: ‘There is poured forth in our hearts the charity of God, by which the whole Trinity inhabits us.’”
Quotations from Francis Cassilly, A Story of Love, 2d ed. (St. Louis: B. Herder, 1917).