The most important doctrine of our Faith is the Holy Trinity. There is one God in three Persons: Father, Son, and Holy Spirit; “Three Persons equal in power, undivided in glory, yet one single Lord and God” (Preface of the Solemnity of the Most Holy Trinity).

Old and new

The important message of the Old Testament is that God is one, and the important message of the New Testament is that God is three.

The most important parts of the Old Testament are the first five books, the Pentateuch (also called the Five Books of Moses). The key message of the Pentateuch is that there is only one God.

The Book of Genesis teaches us that all things in heaven, on earth, and in the water were created by the one true God. An important highlight of the Pentateuch is the Ten Commandments, and the first Commandment is “I am the Lord your God; you shall not have strange gods before Me.”

In the New Testament, the Son of God Himself revealed to mankind the inner life of God, the communion of the three divine Persons. This is the greatest of all revelations.

One and three

In the Blessed Trinity there is one nature in three Persons. A nature is what someone or something is, whereas a person is who someone is. If you ask me “What are you?” my answer would be “a human being.” If you ask me “Who are you?” my answer would be “Anthony Ho.” The first question has to do with nature and the second with person.

If you ask the Blessed Trinity “What are You?” the answer would be “God.” If you ask the Blessed Trinity “Who are You?” the answer would be “Father, Son, and Holy Spirit.” The nature of the Blessed Trinity is God, and the Persons of the Trinity are Father, Son, and Holy Spirit.

Know and love

God is spirit. The two main operations of a spirit are to know and to love. In God, the divine operations and the distinctions of Persons are inseparable.

God knows. The Father knows Himself perfectly, and His perfect Idea of Himself is God the Son. The Father begets the Son.

God loves. The Father and the Son love each other, and the Holy Spirit is the love between the Father and the Son. The Holy Spirit proceeds from the Father and the Son.

The operations of knowing (begetting) and loving (proceeding) in God are eternal. There is not a single moment that the Father is not the Father. The same applies to the Son and the Holy Spirit.

The three divine Persons are really distinct from one another, but are also one and the same God because all have one and the same divine nature.

Works of God

Since all three divine Persons possess the same divine nature, all three Persons are involved in the works of creation, redemption, and sanctification. However we attribute the work of creation to God the Father, because He is the source of divinity. We attribute the work of redemption to God the Son, because He became incarnate to save us on the cross. We attribute the work of sanctification to the Holy Spirit, because He is the love between the Father and the Son.

The communion of Persons in the Blessed Trinity is the source of all genuine societies and communities. Father John Hardon, S.J., writer of the “Modern Catholic Dictionary,” pointed out that except for the Trinity, there would be no society in existence.

He wrote, “Societies like the family, and the Church, and the state exist only because of God, Who made man, made him according to His own image and likeness. And God, by His very nature, is not a solitary being.”

            「天主聖三」是我們信仰的最重要當信道理 —— 唯一天主有三個位格，即是聖父、聖子和聖神。「三位分明、性體唯一、尊威均等。」（天主聖三節日彌撒的頌謝詞） 

新舊二約

舊約的主要訊息是天主只有一個；而新約的主要訊息是天主共有三位。

舊約中最重要的是「梅瑟五書」。而「梅瑟五書」其中重要的訊息，是指出天主只有一個。當中「創世紀」清楚說明，唯一的天主、造物主，從虛無中創造了天地萬物。「梅瑟五書」的高潮是「十誡」。在「十誡」的第一誡，天主詔告天下：「我是你的天主，除我之外＇不可有別的神。」

新約中，天主聖子親自把天主的內在生活 ——「三位一體」的奧跡，啟示給萬民。那是所有啟示中最大的。

一體中的三位

在聖三內有一個天主性和三個位格 —— 「本性」是指某人或某事的根本本質；例如你問我「你是甚麼？」我會答「我是人」。「位格」是指某人是誰；假如你問我「你是誰」，我會答「我是何庭耀」。第一個問與答是有關本性，第二個純涉個體。

如果你問天主聖三「祢是甚麼？」答案是「我是天主」，你若問天主聖三「祢是誰」，答案會是「我們是聖父、聖子、聖神」。聖三的本性是天主，並有三個位格 —— 是聖父、聖子及聖神。

認識和愛

天主是神體，認識和愛是神體的主要活動。在天主內，這些活動和位格是分不開的。

天父完滿地認識自己。衪的完滿而無限的智慧就是天主聖子。聖子由天父所生。

聖父和聖子彼此相愛，聖神就是父與子之間的愛 —— 聖神是聖父聖子所共發。

「認識（生）」和「愛（共發）」，兩者均在天主之內，同為永恆，絲毫不會改變，絲毫不會停止下來。因此，聖父無一刻不是聖父，聖子無一刻不是聖子，聖神無一刻不是聖神。

三位在位格上有分別；但論本性，三位共有同一的天主性 —— 是一性、一體、一個天主。

天主的化工

三位一體的天主是同一的神體，故此，創造、救贖和聖化，皆源自三個位格的唯一天主。但我們慣常認識聖父為「創造者」，因為祂是天主性之源；我們認識聖子為「救世者」，因為祂降生成人，救贖了普世；我們認識聖神為「聖化者」，因為祂是聖父和聖子之間的愛。

天主聖三的共融相通，成了我們現世社會或群體的團結之源或典範。「耶穌會」會士、若望.赫頓神父指出，除非天主聖三，沒有社會存活；他寫道：「家庭、教會或社會沒有天主，都不能牢固存活，因為祂以自己的肖像創造了人類；而祂的本性，並非孤獨自存。」