What do Catholics mean by the Holy Trinity?

We believe in ONE God, who is eternally existent in three divine Persons: Father, Son and Holy Spirit.¹ This is the teaching of the Holy Scriptures² and the early Church. The first Christians gave their lives for this faith. As Justin Martyr wrote in AD 155: “Our teacher of these things is Jesus Christ, who also was born for this purpose, and was crucified under Pontius Pilate, procurator of Judaea, in the times of Tiberius Caesar; and that we reasonably worship Him, having learned that He is the Son of the true God Himself, and holding Him in the second place, and the prophetic Spirit in the third, we will prove.”³

The doctrine of the Trinity was taught from the earliest days of the Church, and it’s helpful to remember that the people who gave their lives as martyrs in the Roman circuses (made into human torches and lion food) died believing that Jesus Christ is God, and that he is the second Person of the Holy Trinity. The name “Trinity” was used as early as the third century to briefly describe the triune nature of God. The doctrine was finally defined dogmatically in the early fourth century at the Council of Nicea in response to the Arian heresy.⁴ Thus, the Catholic Christian faith was dogmatically defined as those Christians who maintained belief in the Trinity, as opposed to those who followed Arius in denying the Trinity.

The doctrine of the Trinity is universally accepted by all Christian churches that broke with the Catholic Church in the sixteenth century and thereafter. It is taught by all Christian churches connected to the Catholic Church through history and baptism. It is the universal doctrine of all Protestant denominations: Lutheran, Anglican, Methodist, Reformed, Presbyterian, Baptist, Pentecostal, etc. Evangelicals are staunchly Trinitarian in their belief about God. Christianity has always been defined as a Trinitarian faith, meaning the belief in ONE God in three equally divine Persons. There are of course some churches that no longer teach the Trinity. These churches are no longer connected to the Catholic Church, neither through history nor baptism. For that matter, they are no longer connected to Protestantism or Evangelicalism, and most of them have no problem telling you that.

For more information on this, see On the Arian Heresy & On Jehovah’s Witnesses.

1. Catechism of the Catholic Church, paragraphs 232, 234, 237, 261 & 266
2. Matthew 3:16-17; Matthew 28:19; John 1:1; John 8:59-59; John 10:30-33; John 14:26; John 15:26; John 20:28; 2nd Corinthians 13:14; Galatians 4:4-6; Titus 2:13
3. Justin Martyr, First Apology 13
4. In the early fourth century, a rogue priest named Arius introduced the teaching that Jesus Christ is not divine and that God is not a Trinity. This caused such a great disturbance in the early Church that an ecumenical council was called in the City of Nicea (located in Asia Minor) in which all of the bishops were summoned to investigate this matter. They condemned the Arian heresy, affirmed the Trinity as the universal faith taught by the Apostles, formulated the Nicene Creed, and ordered the compilation of a universal New Testament to combat this heresy.

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