From his catechism, which for a very long time was the most influential catechism in publication:
S. In what arrangement are these mysteries understood in the most holy sign of the Cross?
T. When we make the most holy sign of the cross we say, "In the name of the Father, and of the Son, and of the Holy Spirit," and we sign ourselves in the manner of the cross. We touch our forehead with our right hand while saying, "In the name of the Father," next the breast when saying, "of the Son," and lastly, we raise our right hand, moving it from the left shoulder to the right while saying, "and of the Holy Spirit." The phrase "in the name of," signifies the unity of God, for we say, "in the name," not names; likewise, it shows the Divine Power that is in the three persons alone. Next, the words, "of the Father and the Son and the Holy Spirit," point out the persons of the Trinity. Moreover, the manner of signing oneself with a cross not only represents the Passion, but consequently also the Incarnation of the Son of God. The progression from the left to the right shoulder (but not from right to left), while using the right hand means we have been transported from transitory to eternal things, and from death to life.
[Robert Bellarmine, Doctrina Christiana, Ryan Grant, tr. Mediatrix Press (2016) pp. 8-9.]