The central doctrine of the Catholic faith is the mystery of the Holy Trinity.
‘The history of salvation is identical with the history of the way and the plan by which God, true and one, The Father, the Son, and the Holy Spirit, reveals Himself to men, and reconciles and unites with himself those turned away from sin’ (Vatican General Catechetical Directory).
The Holy Trinity is in the strictest sense of the word a mystery of faith. It is one of those incomprehensible realities that the First Vatican Council in its Dogmatic Constitution on the Catholic Faith describes as ‘hidden in God which, unless divinely revealed, could not come to be known’.
The fact that incomprehensible realities such as the Trinity can be grasped only by faith is in no way an affront to human reason. Divine mysteries are not contrary to human reason, nor are they incompatible with rational thought. Even in our relationship with other human persons, we must fall back upon faith – a form of human faith – to know the truth of their inmost lives and their love for us. When we speak of the inner life of God, it is a life so far beyond us that we can never completely and fully comprehend its true meaning. But, through faith, we can nonetheless be aware of the truth that God tells us about himself.
Centuries ago, St. Thomas Aquinas pointed out that ‘it is impossible to believe explicitly in the mystery of Christ without faith in the Trinity, for the mystery of Christ includes that the Son of God took flesh, that he renewed the world through the grace of the Holy Spirit, and again, that he was conceived by the Holy Spirit’. Obviously, we could not believe that Jesus is the Son of God and true God sent by the Father if we did not believe in the plurality of persons in one God. Neither would we be able to understand the meaning of eternal life, nor the grace that leads to it, without believing in the Trinity, for grace and eternal life are a sharing in the life of the most Holy Trinity.
The importance of the Trinity in Catholic teaching is evident from the beginning of the Church. When Christ sent the apostles forth to go and ‘make disciples of all nations’, He instructed them to baptize in the name of the Trinity: ‘baptizing them in the name of the Father, and of the Son, and of the Holy Spirit’ (Matt 28:19). From the earliest centuries of the Church and in the most ancient professions of faith, we find a belief in the Trinity of the Father, the Son, and the Holy Spirit. The Athanasian Creed which dates from the fourth century, declares: ‘No the Catholic faith is this: that we worship one God in the Trinity, and the Trinity in unity … the Father is a distinct person, the Son is a distinct person, and the Holy Spirit is a distinct person, but the Father and the Son and the Holy Spirit have one divinity, equal glory and co-eternal majesty’.
The doctrine of the Trinity was not revealed with full clarity at the very beginning of God’s revelation to us. Only gradually, step by step, did God make known to His people the mystery of His inner life. What the New Testament teaches us is captured with clarity and reverence in the statements of the early councils of the Church that we use today: the Apostles’ Creed, the Nicene Creed, the Athanasian Creed.
The preface for the Mass on Holy Trinity Sunday summarizes our belief in what God has told us about Himself: ‘We joyfully proclaim our faith in the mysteries of your Godhead. You have revealed your glory as the glory also of your Son and of the Holy Spirit: three persons equal in majesty, undivided in splendor, yet one Lord, one God, ever to be adored in your everlasting glory’ (Roman Missal).