(From Pastoral Letter of Bishop Javier Echevarria, 1 June 2012):
And so that we don’t forget, amid the ups and downs of life, the joyful destiny that awaits us, the liturgy invites us to celebrate and contemplate, next Sunday, the mystery of the Most Holy Trinity: one God in three Persons, whose definitive possession and enjoyment will bring us the goal of our existence. Let us prepare as well as possible for this solemnity.
Following an ancient custom in the Church, Saint Josemaria recommended that for three days in the Centers of the Work we pray the Trisagium Angelicum. This prayer impels us to participate intimately in the prayer of praise, thanksgiving and glorification that the angels and the blessed souls address incessantly to our triune God. Those of us who had the opportunity of praying it with our Father saw his joy when praising the three divine Persons during the decades of the prayer.
Tibi laus, Tibi Gloria, Tibi gratiarum actio in saecula sempiterna, O Beata Trinitas! We will once again invoke God with these words during this Triduum, directing our prayer to the Father, Son and Holy Spirit. To thee, O Blessed Trinity, be praise, and glory, and thanksgiving, for ever and ever! And we will unite ourselves to the song of heaven, while we repeat: Sanctus, Sanctus, Sanctus Dominus Deus exercituum… Holy, Holy, Holy, Lord God of hosts. Heaven and earth are filled with your glory.
It is very significant that, precisely upon once again beginning ordinary liturgical time, the Church invites us to raise our heart, our voice and our eyes to the Most Holy Trinity. This should be the ambition of all men and women while still here on earth, because we were created to know and love God now and to enjoy him afterwards for all eternity.
In the video above, Saint Josemaria speaks about how each soul in grace is a temple of the Trinity.
The Eucharist and the Mystery of the Trinity (from a homily by Saint Josemaria)
That Trinitarian Current of Love (article about the Holy Trinity)