What do we mean when we say God is a trinity?
“According to the foreknowledge of God the Father and set apart by the Spirit for obedience and for the sprinkling with the blood of Jesus Christ.”
— 1st Peter 1:2
God expresses Himself in three Persons – Father, Son, and Holy Spirit.
While each Person of the Trinity has distinct qualities, all three Persons of the Trinity are made of the same stuff. Each Person is fully God, not one-third God. You cannot divide the Trinity; there is only one God.
(Taken from “Know the Truth:60 Questions and Answers on Christian Beliefs” from First Baptist Church in Tallassee, Alabama; Based on the 2000 Baptist Faith & Message)