Biblical defense of the Trinity
We express the doctrine of the Trinity basically by saying that there is one God in three persons who are equal in substance and glory. The Westminster Shorter Catechism says:
Question 5. Are there more gods than one?
Answer: There is but one only, the living and true God.
Question 6. How many persons are there in the Godhead?
Answer: There are three persons in the Godhead: the Father, Son, and Holy Spirit; and these three are one God, the same in substance, equal in power and glory.