Though the word "Trinity" is not in the Bible, it is filled with many passages demonstrating its reality. In fact, we are baptized as Matthew describes:
"And Jesus came and said to them, 'All authority in heaven and on earth has been given to me. 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, teaching them to observe all that I have commanded you; and lo, I am with you always, to the close of the age.'" Matthew 28:18-20.
Jesus said, "...in the name of..." rather than, "...in the names of..." And there are many, many more.
This is a wonderful example of Catholic Sacred Tradition; it does not create doctrine, but rather reflects a deepening of our understanding through the Holy Spirit. The origins of the Holy Trinity to describe the relationship of the Father, the Son, and the Holy Spirit go back to St. Theophilus when he uses the word Triad around the year 180.
Here is some artwork relating to the Holy Trinity.
The Adoration of the Holy Trinity by Albrecht Durer, 1511. Oil on panel. Kunsthistorisches Museum, Vienna, Austria
The Holy Trinity by El Greco, 1577, paint on canvas, Museo del Prado, Madrid
Trinity is the towering centerpiece of a major renovation at Trinity Lutheran Church in Moorhead, Minnesota.
Trinity by Andrei Rublyov c. 1411, tempera on panel, Tretyakov Gallery, Moscow (An example of the Byzantine representation of the the Holy Trinity as three men)
In the name of the Father, the Son, and the Holy Spirit. Amen.
