Understanding the Doctrine of the Trinity

The first Sunday after Pentecost is known as the Solemnity of The Most Holy Trinity, focusing on the doctrine that God is three Persons in one.

What Is the Doctrine of the Trinity?

The doctrine of the Trinity is a profound mystery and can be difficult to understand; however, the Athanasian Creed provides a good summary:

We worship one God in Trinity, and Trinity in Unity; neither confounding the Persons, nor dividing the Essence. For there is one Person of the Father; another of the Son; and another of the Holy Ghost. But the Godhead of the Father, of the Son, and of the Holy Ghost, is all one; the Glory equal, the Majesty coeternal…

In short, God is one God, in three distinct persons, each with different roles. God the Father is unbegotten, and he sent Jesus, his only-begotten Son, to be the propitiation for our sins. The Holy Spirit is our advocate, sent from both the Father and the Son to reveal the Gospel to us.

The Trinity in the Old Testament

Though the Bible does not specifically use the term “trinity,” the idea is found throughout Scripture, in both the Old and New Testament. Genesis 1:1-2 describes the Trinity being involved in creation:

God created the heavens and the earth. The earth was without form and void, and darkness was upon the face of the deep; and the Spirit of God was moving over the face of the waters.

In multiple places, the Psalms describe Jesus as the Son of God, including Psalm 2:7-8

I will proclaim the decree of the Lord,
    he said to me, “You are my son;
    today I have begotten you.
Ask it of me,
    and I will give you the nations as your inheritance,
    and, as your possession, the ends of the earth.”

The Trinity in the New Testament

In the New Testament, the Trinity is vividly shown in the baptism of Christ:

It happened in those days that Jesus came from Nazareth of Galilee and was baptized in the Jordan by John. On coming up out of the water he saw the heavens being torn open and the Spirit, like a dove, descending upon him. And a voice came from the heavens, “You are my beloved Son; with you I am well pleased.” (Mark 1:9-11)

In this event, the Son was baptized, the Holy Spirit descended, and the Father spoke from the heavens. The Father and the Holy Spirit confirmed the deity of Christ, while Christ submitted to his Father’s will.

During his earthly ministry, Christ also declared, “The Father and I are one,” pointing to his unity with the Father (John 10:30).

The Trinity at the Basilica

The Trinity is depicted at the Basilica in the Trinity Dome and in the Trinity Dome stained glass windows. Various symbolic representations are found throughout the Basilica as well, including the fleur-de-lis of the Great Dome, the Triquetra (three-cornered Celtic symbol) in the arch of the South Façade, and the Tintinnabula (bell emblem).

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