You can find out about their history and apostolate at their website, excerpt:
The Society of Our Lady of the Most Holy Trinity (SOLT) is a Society Of Apostolic Life comprised of Priests, Brothers, Deacons, Sisters, and Laity. Our primary Apostolate is to serve the areas of deepest apostolic need. We serve in missions across the world in the following specific areas of apostolate: parishes, migrants and refugees, education, catechetics, evangelization, ecumenism, healing, drug addiction, prisons, government, military, promoting peace and justice, marriage and family life, youth, abandoned and homeless children, the poor and destitute.
Our charism (the gift that our community gives to the world) is ecclesial or family teams. When we serve at a mission, we strive to serve with our SOLT priests and brothers, SOLT Sisters, and SOLT laity, thereby witnessing how the Trinity lives, as three persons in One God. We live as three vocations in one family. The Society of Our Lady of the Most Holy Trinity (SOLT) was founded in 1958 by Fr. James Flanagan.
Of course, no prior familiarity is required to appreciate Bishop Robert W. Finn's inspiring homily at their Anniversary Mass:
Dear Father Flanagan
Father Albano and Fr. Sheehan
Dear Members of the Society: brother priests and deacons,
Cherished Religious and bold lay apostles,
Friends in Christ All,
It is a joy to welcome you here to the Cathedral and celebrate with you, in the context of the eternal sacrifice of Jesus Christ in the Mass, this grace of 50 years. It is a grace given to you by God, who has made the Society your life-long vocation. Your far-reaching missionary zeal, and the heavenly Communion of members who have already gone ahead of you, marks your holy and Catholic status within the Church and must be a cause of hope for you as you take up the next half-century.
We celebrate also a powerful grace of discernment and obedience in the mind and heart of your Founder, Father James Flanagan. With perseverance this young priest followed the impulse of our Blessed Mother’s love more than 50 years ago. Together with Fr. McHugh and the first Sisters, and with the confirmation of the holy Franciscan Father Solanus Casey, he embarked on a daring journey to model the dynamic and loving communion of the Holy Trinity through the interaction of priests, Religious and laity: all this even before the Second Vatican Council, and Lumen Gentium!
Yours is a grace granted to the Church who sees revealed in your faith and love an image of Mary, Our Lady, Daughter of the Father, Mother of the Son, Spouse of the Holy Spirit – certainly the most magnificent human heart ever created, in which dwells the fire and purity of a Triune love. Under her mantel you have received protection and contagious confidence.
Yours is a grace that has also been extended, by God’s mercy and providence, to this Diocese, where with a missionary heart you continue to serve in humility and devotion. Praise be to God, Father, Son and Holy Spirit.
I thank you for the witness of your zeal and for a family spirit which you bring to our local Church, and in a personal way you have extended to me on so many occasions. Well do I remember what was probably my first encounter with the Society, when after Mass we sat together for some hours on Tracy Street, hearing about the history of your Society, talking for a long time about our dreams for a new evangelization, and sharing a huge family meal – almost like Thanksgiving.
This past summer more than 25 thousand faithful from this Diocese, our neighbor to the West, and others throughout the Midwest, gathered in Royals Stadium to adore our Eucharistic Lord and lift a Global Living Rosary for peace in our world, again, an initiative of the Society. This week, I was able to visit with Fr. Sheehan, your Regional Priest Servant, about the potential expansion of your work among the poor of our Diocese. Later this month I will again have the blessing of sharing a time of prayer for Healing and Forgiveness initiated by members of the Society. I know God has directed and will continue to guide every detail of these efforts. How can I help but give thanks for the generosity and faith which you bring to the People of God here?
St. Paul exhorts and encourages us today, “Do everything without grumbling or questioning, children of God, in the midst of a crooked and perverse generation among whom you shine like lights in the world.” (Phil 2:15). We know all too well the darkness of the culture which surrounds us. Our Lord came into this darkness, under the heart of Mary. Through the Cross He pierced the cloak of sin and death. We know the cost of following Him is a share in that Cross. At the same time He supports us with co-disciples in the work of building the Kingdom, and an unconquerable hope of ultimate victory. Dear friends, you are lights for me, and welcome co-workers. I know God will use us all for His glory.
While I am very thankful for the ministry of your priests, which secures many spiritual gifts for the people – especially the Mass and Confession, I want to acknowledge briefly the unique vision of lay apostolate that I see in the Society.
Since the Council there remains much confusion in the Church about the distinctive and complementary roles of clergy, Religious and laity. Too often the laity have been misdirected to one or other degree in a confusion of ordained and baptismal priesthood. The work of the lay faithful, rather, is a mission no less than the transformation of the culture from the inside out. Yes, some lay members will serve in functions around the altar and as representatives of the institutional Church. But 97% of the lay faithful must live as leaven in the world, in every facet of the life of man.
Bishop, priest, deacon, consecrated Religious must all do their part. Without the laity bringing an active faith into every field of human endeavor the work of the Kingdom would remain incomplete, and the establishment of that civilization of life and love, about which the Gospel speaks with such hope, will be delayed. I want to say simply that, over and over again I see that SOLT gets this right! What an exciting prospect this holds, when the dignity of the lay vocation is recognized alongside the priest and Religious, without competition. In this way alone can each diverse part of the Body be acknowledged in its giftedness, and enabled to fulfill its necessary complementarity. As the Most Blessed Trinity Itself is One God - three distinct Persons, so also we sense a resemblance of this most sublime mystery in the integral unity of the members of Body of the Church.
Vital to your calling is, likewise, that deep interiority which was Mary’s. The indwelling love and fire of the Holy Trinity informs and animates your societal communion and your apostolic action. We want to love others in accord with a supernatural grace. The virtues manifested in the Incarnate Christ, the gifts of the Holy Spirit, and a powerful sense of our Divine Filiation, our freedom as the children of the Father: These are the riches that are lasting and salvific for the life of the Church. Without holiness, the energy of natural goodness would wane quickly, and it seems unlikely that mere human cleverness can move hearts that are weighed down with the cares and trials of the world.
In today’s Gospel Our Lord challenges us to take stock of our resources, to count our troops before going into battle. Let us not for a moment forget that, as members of the Church Militant, we are engaged, not against mere flesh and blood, but against “principalities and powers.” Clearly we must arm ourselves with God’s grace and holiness, a share in His very life without which we could never hope to endure.
Yours today is a Golden Grace, a steady light which has its source in Jesus Christ and which is wondrously reflected in Our Lady. It is my joy to join with you and your Founder in this Jubilee celebration. May the work of your Society continue to the Glory of the Most Holy Trinity and the help of the Church.