This is the last paper I wrote for my Trinitarian theology class. Never got around to posting it.
The Gospel of John could rightly be called the Gospel of Divine Mystery. In it appears, perhaps, the most direct and well-known expression of the Incarnation in all of the New Testament: “And the Word became flesh and dwelt among us, full of grace and truth; and we have beheld his glory, glory as of the only Son from the Father” (1:14). It is through the Son that we come to know the Father (1:18). By John’s gospel message, we come to know of Father, Son, and Holy Spirit and the indwelling of God in us. Fr. Kenneth Baker refers to three absolute mysteries in Catholic theology: the Trinity, the Incarnation, and divine grace. In the Gospel of John, one comes to a deeper appreciation of all three. Yet the terminology we use to discuss these mysteries more deeply comes not out of the gospel account alone, but the works of the Fathers, Doctors, and theologians throughout our tradition.
Believers can only know the Trinity through Divine Revelation. Based on revelation, the early Church Fathers came to an understanding that the internal life of God was triune, and that within the Unity of the Divine Essence subsisted three relations, three Divine Persons. The Council Fathers at Nicaea identified the relations of paternity and filiation in their discussions on the generation of Christ (Denzinger 54), a position clearly enunciated in scripture. Fifty-six years later, the Council of Constantinople proclaimed the procession of the Holy Spirit from the Father (Denzinger 86), a doctrine reiterated by the Decree of Damasus at the Council of Rome one year later (Denzinger 83). The Council of Toledo in 693 (Denzinger 296) would then later proclaim that procession of the Holy Spirit is from both Father and Son, a position that would later put the Eastern and Western Churches at odds.
How, then, does one come to understand the external actions of God in regards to humanity? As Fr. Baker puts it, “What does the doctrine of the Trinity have to do with me and the very practical problems I must face every day?” Perhaps another way to ask these questions is, just how does God reveal Himself to us? Once He does, how do we come to accept Who He is, and how does accepting Him help us to choose what is truly good? How does God come to us, and once here, dwell with us?
We refer to the sending of Divine Persons into the world as missions (from the Latin word missio). Scripture attests repeatedly to the sending of both Son and Holy Spirit. In John 3:17, the evangelist relates that the Son was sent and notes the reason for His sending: “For God sent the Son into the world, not to condemn the world, but that the world might be saved through him.” At His last supper with the Apostles, Jesus tells of the sending of the Holy Spirit: “‘These things I have spoken to you, while I am still with you. But the Counselor, the Holy Spirit, whom the Father will send in my name, he will teach you all things, and bring to your remembrance all that I have said to you’” (14:25–26). So both Son and Holy Spirit have been sent, and each has a particular role to play unique to His sending. Each is sent, as well, according to the particular character of His own procession and origin. As the Catechism of the Catholic Church states,
[E]ach divine person performs the common work according to his unique personal property. Thus the Church confesses, following the New Testament, “one God and Father from whom all things are, and one Lord Jesus Christ, through whom all things are, and one Holy Spirit in whom all things are”. It is above all the divine missions of the Son’s Incarnation and the gift of the Holy Spirit that show forth the properties of the divine persons. (258)
The notion of mission, according to St. Thomas, includes both the relation of the one sent to the one who sends and the relation of the one sent to the term of the sending (I, 43, 1). The relation of sent to sender in divine Persons is one of origin, as in no way can the relation suggest inferiority on the part of the One sent. But if God is present everywhere, how does the sending of a Divine Person affect or change the relation of the One sent to those to whom He is sent? The Divine Person does not change, does not cease to be present where He is, and does not become present where He was not. He who is sent becomes present to the term in a new, unique way.
The missions correspond in some way to the personal relation of those Who are sent and the One Who sends. The Father sends the Son, and the Father and Son send the Holy Spirit, as mentioned previously. In this sense, being sent resembles procession from an origin. Yet, procession by way of generation and passive spiration are internal and eternal activities in God. Mission, in contrast, takes place in time. It is a temporal “being here” in the world, an external procession into the life of mankind (I, 43, 2). Ludwig Ott writes, “The temporal missions, therefore, reflect the ‘notions’ of the Divine Persons. The Father sends only, but is not sent; the Son is sent and sends; The Holy Ghost is sent only, and does not send.”
Of missions, theologians speak of those that are invisible and those that are visible, depending on whether the mission is perceptible to the senses or not. When one thinks of visible missions of Christ and the Holy Spirit, one thinks first of the Incarnation, the presence of God made flesh in our world, then of the appearance of the Holy Spirit in the form of a dove at the baptism of Christ and later as tongues of flame during the Pentecost following Christ’s resurrection. Nonetheless, the two visible missions differ in kind as well as origin. As St. Thomas notes, while the Son took on a human nature and assumed it into the unity of His Person, the Holy Spirit only appeared visibly as signs that passed once His purpose was accomplished. These visible missions, he posits, are necessary for humanity because human nature is such that mankind must be led to the invisible through the visible (I, 43, 7). So the mode of Christ’s visible mission was befitting to the author of our sanctification, while the mode of the Holy Spirit’s visible mission was befitting to signs of that sanctification.
These visible missions point to the invisible missions. Christ refers to these invisible missions in John 14:16–17: “‘And I will pray to the Father, and he will give you another Counselor, to be with you forever, even the Spirit of truth, whom the world cannot receive, because it neither sees him nor knows him; you know him, for he dwells with you, and will be in you.’” Again, just verses later He adds, “‘[W]e will come to him and make our home with him’” (14:23). With these invisible missions, the Father, Son, and Holy Spirit come to dwell in the soul of the believer. This indwelling of the Holy Trinity begins in the faithful a new life through sanctifying grace. Fr. Baker explains that “[t]he full meaning of sanctifying grace is that God Himself, that is the Holy Trinity… is personally present in me in a way that he is not present in the rest of the material universe.” While only the Son and the Holy Spirit are sent, the missions are the activity of the entire Trinity, so that the whole Trinity comes to reside in the soul of the sanctified. God’s presence in the soul sanctifies the believer, enables the believer to be more open to receiving grace, more open to knowledge of Him, and by knowing, more open to loving Him.
All things are created by God, and all things must return to Him. The Trinity is the source of all things and the final end or purpose. The fall of our original parents and the damage in human nature due to original sin necessitated humanity’s redemption. Only through sanctifying grace and the indwelling of the Holy Trinity in the souls of the faithful can fallen human nature be set to that end again. Through sanctifying grace, the believer is divinized, made a temple of God, and an adopted son or daughter of God.  As images of God and heirs, mankind too has a share in the missions.
In the Gospel According to Matthew, Jesus sends out the Twelve to heal and to cast out demons (10:1). He prepares the Apostles for their missions, saying, “He who receives you receives me, and he who receives me receives him who sent me” (10:40), and in the Gospel According to Luke, in a parallel passage, Jesus sends out seventy disciples and says “He who hears you hears me, and he who rejects you rejects me, and he who rejects me rejects him who sent me” (10:16). Fittingly, as the Son was sent, so He sends us. God dwells in us to sanctify us to send us into the world. In Matthew 28, Jesus sends the remnant of the Twelve once again in the Great Commission: “Go therefore and make disciples of all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Spirit.” We celebrate this commission at the conclusion of every Eucharistic liturgy. He was sent to us, and He sends us into the world to complete His work of sanctification by announcing His good news.
Aquinas, Thomas. “Summa Theologica, Prima Pars.” New Advent. 2000. http://www.newadvent.org/summa/1027.htm (accessed October 6, 2011).
Baker, Kenneth. Fundamentals of Catholicism. San Francisco: Ignatius, 1983.
Catechism of the Catholic Church. Washington D.C.: United States Catholic Conference, 1997.
Denzinger, Henry. The Sources of Catholic Dogma. Fitzwilliam, New Hampshire: Loreto Publications, 1954.
Hardon, John. “Modern Catholic Dictionary.” Real Presence Eucharistic Education and Adoration Society. 2011. http://www.therealpresence.org/cgi-bin/getdefinition.pl (accessed December 8, 2011).
Ott, Ludwig. Fundamentals of Catholic Dogma. Rockford, Illinois: Tan Books and Publishers, Inc., 1974.
 Kenneth Baker, Fundamentals of Catholicism, (San Francisco: Ignatius, 1983) 79.
 Ibid., 112.
 Fr. John Hardon, “Modern Catholic Dictionary,” Real Presence Eucharistic Education and Adoration Society, 2011, http://www.therealpresence.org/cgi-bin/getdefinition.pl (accessed December 8, 2011).
 Ludwig Ott, Fundamentals of Catholic Dogma, (Rockford, Illinois: Tan Books and Publishers, Inc., 1974), 73.
 Ibid., 74.
 Baker, 112.
 Ibid., 114.
 Ibid., 113–114.