A deep mastery trainer for the doctrine of the Trinity. One God, eternally three distinct persons — Father, Son, and Holy Spirit. Definitions, the deity and distinction of each person, the biblical foundation and memory verses, the Old Testament background, the classical vocabulary (ousia, hypostasis, eternal generation, procession, perichoresis, simplicity), the councils and creeds (Nicaea, Constantinople, Athanasian, Reformed confessions), the historic heresies, the objections (Jewish, Islamic, Jehovah's Witness, feminist, Ehrman/evolutionary), the social-vs-Latin models, the gospel necessity, and worship. Each mode trains a different skill; the final exam ranges over the whole bank. Unlock each subtopic by scoring at least 90% on its mastery check.