On the night of his betrayal, Jesus shared some of the most personal moments of His ministry with His disciples. The scenes, as chronicled by the evangelists, are affectionate and moving. Christ stooped to wash the disciples’ feet, instituted the sacrament of the Lord’s supper, and conveyed to them words of joy and peace even as He promised that they would one day follow in His foot-steps.

As the disciples’ world was about to be turned upside down, Jesus took that evening to instruct them in some of the most sublime truths of the interrelationship among Father, Son, and Holy Spir-it. To put it simply, His final testimony before enduring the agony of the cross was to comfort the disciples in the doctrine of the Trinity—a doctrine not for lecture halls or ivory towers, but an eter-nal truth that ministers to our deepest needs.

As we have seen, the Westminster Larger Catechism begins teaching on what we are to believe concerning God: who God is and that there is only one God. But a student of the Bible must ap-preciate that Scripture’s teaching goes even deeper into the knowledge of God. The Bible clearly reveals that there is one God (e.g., Deut. 6:4; Rom. 3:30; Gal. 3:20; Jas. 2:19) but its data also points to a three-ness. The Father is identified as God (see Eph. 4:6) but so are the Son and Spirit: to each are attributed divine names (John 8:58 and Acts 5:4), actions (Col. 1:16 and Ps. 33:6), and worship (Matt. 28:9 and Phil. 3:3). The biblical conclusion is that the Father is God, the Son is God, and the Holy Spirit is God.

However, if we take it a step further, we also need to understand that these three—Father, Son, and Spirit—are not the same. For instance, Jesus tells His disciples: “I will ask the Father, and he will give you another Helper, to be with you forever, even the Spirit of truth” (John 14:16–17, emphasis added). Jesus’ words reveal an important truth: He is not the Father, the Father is not the Spirit, and the Spirit is not the Son. These three are distinct. This is, perhaps, most clearly ex-hibited at the Jordan River as Jesus is baptized, the Holy Spirit descends like a dove, and the Father speaks from heaven a word of divine approbation.

If we collect the evidence of the Bible, we are led to this conclusion: the one God is Father, Son, and Holy Spirit. Of course, this can be a head-scratcher. Is it irrational? Fuzzy math? Absurd? Laughable? To this the catholic church—meaning the universal church—devoted considerable at-tention. The earliest centuries of the Christian church carefully interacted with the Scripture to frame the doctrine of the Trinity in language of one in substance and three in person.

There are two important parts to the answer of the catechism’s question. First is the affirmation that Father, Son, and Holy Spirit have, in common, the divine substance—“these three are one, true, eternal God, the same in substance, equal in power and glory.” That is to say, the essence of God (for what He is, see WLC Q. 7) is communicable and common in the unity of His nature to all three persons. Father, Son, and Holy Spirit is all that God is. Second, the catechism begins hinting at the distinction in relations that are incommunicable and particular to each person—“although dis-tinguished by their personal properties” (see WLC Q. 10). When the catechism uses this formu-la, it is expressing consent to the ancient creeds of the apostolic and catholic church.

Admittedly, this can be confusing. When we speak of the doctrine of the Trinity, most of us find ourselves ascending to heights where it gets hard to breathe for lack of oxygen. But there is noth-ing more rewarding than pursuing the knowledge of the triune God. And that reward is personal. After all, as Christians, we have been baptized into the singular name of Father, Son, and Holy Spirit.