This wonderful feast day is a reminder of the mystery of God. The Trinity has always been a confusing idea for me and others, and I certainly don't pretend to have an inkling of understanding this reality. The three leaves on the shamrock help somewhat, but what my Dad told me once helps me even more. My Dad used himself as an example. He is one man, but he is my father, he is his parent's son and he is my mother's spouse. When we think of the Trinity, hopefully we're focusing on relationship. Not only the relationship of God the Father, God the Son and God the Holy Spirit, but our relationship with each in God.
When we make the sign of the cross we are remembering the Godhead.
Lord, we believe, help our unbelief, and help us to cultivate our relationship with you! Amen