Teacher Notes: Unit 3, The Blessed Trinity
Why this unit matters
Most students have heard the Trinity explained with an analogy that is actually a heresy, usually water, ice and steam. Many quietly conclude that the doctrine is either a contradiction or a polite way of saying “we don’t know”. This unit aims to show that the Church’s teaching is precise, consistent and central to Christian life, while remaining a true mystery.
The key move is in Lesson 3.1: one answers the question “what?”, and three answers the question “who?”. If students take only one thing from the unit, it should be that.
By the end of the unit, students should be able to:
- state the doctrine of the Trinity precisely, in one sentence;
- explain why it is not a contradiction, using nature and person;
- identify modalism, Arianism and tritheism, and spot them in popular analogies;
- name the two processions and explain how the Persons are distinguished by relations;
- explain what the Filioque is, and how the Council of Florence related it to the Eastern formula;
- explain appropriation and the missions, and describe how the Trinity shapes prayer and the sacraments.
A shape for a 50-minute lesson
| Time | Activity |
|---|---|
| 5 min | Put the big question on the board. Take three or four answers without correcting them. |
| 15 min | Read What the Church teaches and Where it comes from together. |
| 15 min | Teacher-led explanation, using the lesson’s table. |
| 10 min | Discussion question, or work through What the Church does not claim. |
| 5 min | Students attempt two Check your understanding questions before opening the answers. |
Lesson by lesson
3.1 One God, three Persons
Goal: students can state the doctrine and explain why it is not a contradiction.
Activity: heresy spotting. Give students five popular analogies (water/ice/steam; a three-leaf clover; one man who is a father, son and husband; the sun, its light and its heat; an egg’s shell, white and yolk). Ask them to say which error each one falls into. Most fall into modalism or into dividing God into parts. The point is not that analogies are banned, but that the Trinity has no real equal in creation.
Discussion questions:
- Why does it matter that the Father speaks to the Son at Jesus’ baptism?
- What is lost if Jesus is only the greatest creature, as Arius taught?
Misconceptions to watch for:
- “Three in one is just bad maths.” Use the what/who distinction.
- “Each Person is a third of God.” Each Person is the whole of God.
- “The Holy Spirit is a force or an energy.” Scripture treats the Spirit as a Person who can be lied to, who teaches and who intercedes.
3.2 Processions and relations
Goal: students can name the two processions and explain that relations distinguish the Persons.
This is the most abstract lesson in the course so far. Keep returning to the table. With a younger or less confident group, it is enough that students understand “begotten, not made”, that the Persons are distinguished only by where each comes from, and the basic idea of Augustine’s analogy.
Discussion questions:
- Could someone be a father without having a child? What does that show about how the Persons are distinguished?
- Why does Augustine look for an image of the Trinity in the human mind rather than in nature?
Ecumenical note. Some students will have Orthodox friends or relatives. Present the Filioque as a real disagreement that both churches take seriously, and stress the Council of Florence’s point that the two formulas can express the same truth. Avoid presenting either church as simply wrong.
Misconceptions to watch for:
- “The Father existed first and then had a Son.” Begotten eternally.
- “The Filioque means the Spirit has two sources.” One principle, one spiration.
3.3 The Trinity and us
Goal: students can explain appropriation and the missions, and connect the Trinity to prayer and the sacraments.
Activity: give students the text of a Collect from Sunday Mass and ask them to find the three Persons in its ending (“through our Lord Jesus Christ, your Son, who lives and reigns with you in the unity of the Holy Spirit”). Then do the same with the Glory Be and the sign of the cross.
Discussion questions:
- What would be different about love if God were one solitary Person?
- Jesus says the Father and he will “make our home” with those who love him. What does it mean for a person to be a dwelling place of God?
Misconceptions to watch for:
- “The Father created, the Son saved, and the Spirit makes us holy, separately.” These are appropriations; all three act in each.
- “The Trinity is only for theologians.” Point to the sign of the cross, baptism, and the Our Father.
Answer key
The answers to every Check your understanding question also appear on the lesson pages behind Show answer, and are left off printed handouts.
Lesson 3.1: (1) One God in three really distinct Persons, each fully God. (2) One in nature, three in person: different respects. (3) Modalism: one Person, three modes. Arianism: the Son is a creature. Tritheism: three gods. (4) “With God” shows distinction; “was God” shows divinity. (5) It suggests one thing in three forms, which is modalism.
Lesson 3.2: (1) Generation (the Son) and spiration (the Holy Spirit). (2) Only their relations of origin. (3) The mind, its knowledge of itself and its love of itself: one mind, three acts. (4) “And the Son”; Florence held it and “through the Son” express the same truth, the Father being the source without source. (5) No; the Son is begotten eternally.
Lesson 3.3: (1) The three Persons are one principle of all God’s outward works. (2) Attributing a common work to one Person by likeness, such as creation to the Father. (3) A procession is eternal origin; a mission is being sent into the world in time. (4) John 14:23 (also 1 Corinthians 6:19). (5) Any two of: baptism, prayer through the Son in the Spirit, adoption, heaven, the sign of the cross.