The doctrine of the Trinity is foundational to the Christian faith. It is crucial for properly understanding what God is like, how he relates to us, and how we should relate to him. But it also raises many difficult questions. How can God be both one and three? Is the Trinity a contradiction? If Jesus is God, why do the Gospels record instances where he prayed to God?
While we cannot fully understand everything about the Trinity (or anything else), it is possible to answer questions like these and come to a solid grasp of what it means for God to be three in one.
One God, Three Persons
The doctrine of the Trinity means that there is one God who eternally exists as three distinct Persons — the Father, Son, and Holy Spirit. Stated differently, God is one in essence and three in person. These definitions express three crucial truths: (1) the Father, Son, and Holy Spirit are distinct Persons, (2) each Person is fully God, (3) there is only one God.
The Father, Son, and Holy Spirit are distinct Persons. The Bible speaks of the Father as God (Philippians 1:2), Jesus as God (Titus 2:13), and the Holy Spirit as God (Acts 5:3–4). Are these just three different ways of looking at God, or simply ways of referring to three different roles that God plays? The answer must be no, because the Bible also indicates that the Father, Son, and Holy Spirit are distinct Persons.
For example, since the Father sent the Son into the world (John 3:16), he cannot be the same person as the Son. Likewise, after the Son returned to the Father (John 16:10), the Father and the Son sent the Holy Spirit into the world (John 14:26; Acts 2:33). Therefore, the Holy Spirit must be distinct from the Father and the Son.