How do you grasp (to whatever extent) the mystery of the Trinity? For a historical look at the matter, I strongly suggest you read the Athanasian Creed (Quicumque vult); in it, St. Athanasius -- the champion of Trinitarian Christianity against the oppression of Arius -- very clearly and explicitly describes the three Person, their relationships to one another, their substance, their nature, their being, etc. It sacrifices prolixity for unambiguity; it is verbose and unequivocal.
I'll supply a few sub-topics for conversation.
- What verses in Scripture support the doctrine of the Trinity? Which verses seem to hinder it?
- What do we mean when we say that God is three "persons"?
- How can we infer that God is at least two "persons" from St. John's statement that "God is love" (1 John 4:8,16)?
- Why are the canonical names of the three Persons in the Trinity -- Father, Son, and Holy Spirit (or Ghost) -- the best names to use? That is, how are they better than names such as "Creator", "Redeemer", and "Sanctifier"?
- How are the three Persons of the Trinity related to one another? Specifically, where does the Holy Spirit come into the equation? (St. Thomas Aquinas to the rescue! Preface, 1, 2, 3, 4, 5, Note)