The doctrine of the Trinity is encapsulated in Matthew 28:19, where Jesus instructs the apostles: “Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit.”
The parallelism of the Father, the Son, and the Spirit is not unique to Matthew’s Gospel, but appears elsewhere in the New Testament (e.g., 2 Cor. 13:14, Heb. 9:14), as well as in the writings of the earliest Christians, who clearly understood them in the sense that we do today—that the Father, the Son, and the Spirit are three divine persons who are one divine being (God). (Robert H. Brom, Bishop San Diego, 2004)
Trinity Prayer (Fr. Richard Rohr)
God for us, we call You Father,
God alongside us, we call You Jesus,
God within us, we call You Holy Spirit.
You are the Eternal Mystery
that enables, enfolds, and enlivens all things,
even us, and even me.
Every name falls short of your
Goodness and Greatness.
We can only see who You are in what is.
We ask for such perfect seeing.
As it was in the beginning, is now,
and ever shall be.