As the Holy Trinity, our God is One Being, although Three Persons, so, likewise, we ourselves must be one. As our God is indivisible, we also must be indivisible, as though we were one man, one mind, one will, one heart, one goodness, without the smallest admixture of malice – in a word, one pure love, as God is Love. “That they may be one, even as We are One.” (St. John 17:22) ~ St. John of Kronstadt.
…we shall begin… by applying identical expressions to the Three. ‘He was the true light that enlightens every man coming into the world’ (St. John 1:9) – yes, the Father. ‘He was the true light that enlightens every man coming into the world’ -yes, the Son. ‘He was the true light that enlightens every man coming into the world’ -yes, the Comforter. These are the three subjects and three verbs – He was and He was and He was. But a single reality was. There are three predicates – light and light and light. But the light is one, God is one. This is the beginning of David’s prophetic vision: ‘In Your light shall we see light’ (Psalm 36:9). We receive the Son’s light from the Father’s light in the light of the Spirit: that is what we ourselves have seen and what we now proclaim – it is the plain and simple explanation of the Trinity. ~St. Gregory Nazianzus (On Christ and God, Oration 31:3)
The three-leafed shamrock on a single stem, was used by 5th century St. Patrick to illustrate the Holy Trinity – our One God in Three Persons. St. Patrick wrote many hymns. Here is a short excerpt from a longer, beautiful hymn. “I bind unto myself today, the Strong Name of the Trinity! By Invocation of the same, the Three in One, and One in Three!”