Our belief in Christ, the call to make disciples, our salvation, and our prayers are all rooted in the triune nature of God. The Trinity, brothers and sisters, is not a doctrine to be left to the theologians for scholarly discussion. This is the nature of our great God and Savior. This is who the one true and living God is. And the Trinity is infinitely practical to us as we strive in all things to know and love Him more deeply through His Word.
After briefly defining what is God, we now come to the doctrine of the Trinity. To be honest, for several years the phrasing of Question 2 perplexed me (which reflects the fourth question of the Westminster Shorter Catechism). To ask what instead of who makes God seem impersonal. However, we must remember that God is a title; therefore, Question 2 is answering what we are describing with that title. Question 3 is essentially asking who God is, for even the question itself ascribes personality to God. In the Old Testament, God revealed His name, Yahweh, to Israel, and in the New Testament, He has revealed a deep mystery behind His holy name. We call that mystery the Trinity: there are three persons in the one true and living God.
Although this mystery is profound, it is not complicated like a sort of divine mathematical formula. As we defined God in Question 2, we believe that the Father, the Son, and the Holy Spirit are each fully God. They are the same in substance, equal in power and glory. Furthermore, the Father, the Son, and the Holy Spirit are three distinct persons, so that the Father is not the Son, the Son is not the Holy Spirit, and the Holy Spirit is not the Father. However, the Father, Son, and Holy Spirit are not three Gods, but together are united as the one true and living God. Indeed, as Matthew 28:19 notes, this is God’s name. Yahweh is the Father, the Son, and the Holy Spirit.
How can three be one and one be three? There is the profundity and the grand mystery that must be received by faith. Of course, if God really is infinite, then we should not expect to be able to fully explain every aspect of His divinity. Rather, we ought to bow our heads in humble gratitude that He would reveal such a marvelous truth to us at all.
Of course, since the Trinity is a mystery that will forever elude our full comprehension, many Christians avoid thinking about it at all.