A human being trying to understand the Trinity is like a beetle trying to comprehend the universe. Our brains are just not equipped to handle it. It is a Mystery. One day, when we reach our eternal reward, it may become clear but certainly not while we’re on the this earthly sphere.
The Trinity means that there is only one God. In that one God, there are three Divine persons, God the Father, God the Son and God the Holy Spirit.
St. Patrick used a shamrock leaf to try to explain the concept. He held up a shamrock leaf and asked how many leaves he had. “One,” his listeners answered. Then he asked how many parts there were to the leaf. “Three,” was the reply. St. Patrick explained that that leaf symbolized God- one leaf, three equal but distinct parts.
Other metaphors have been used: three notes played together on a piano produce a single sound; if three lighted matches are held together, you see a single flame. I am one person but I have different roles. To my husband, I am a wife: to my children, I am a mother; to my parents, I am a daughter. The great theologian, Karl Rahner said, “God has three ways of being.”
To each Person of the Trinity is ascribed a different action. God the Father is the Creator, the Originator of the universe, the earth and all that it contains. Old Testament time, from Creation to the birth of Jesus, is known as the Age of the Father.
From the birth of Jesus until Pentecost is known as the Age of the Son. These were the years when Jesus, the Son of God, took on a human body and lived among us. His was the work of salvation. By His suffering and death on the cross, Jesus atoned for every sin which the human race would ever commit.
On Pentecost, the Holy Spirit descended upon and began to indwell the Apostles, giving them the wisdom and strength to begin the Christian Church. Thus began the final age, the Age of the Spirit. During this age, God works mainly through his Spirit, indwelling and inspiring the members of the Church. We are to function as his hands and feet, going about and doing good on earth until Jesus comes again.
This then, in limited human terms, is the Trinity, three Persons in one God. You cannot pray to one Person without the Others hearing, because they are one. Don’t try to comprehend this Mystery, you’ll only get a head-ache. Sometime in the world to come, we’ll get a full explanation.