St Gregory of Nyssa wrote the Catechetical Discourse as a handbook for his catechists, to help them defend and articulate the foundations of the faith, the Trinity, creation and the image of God, the fall and the nature of evil, the saving work of Christ, and the sacraments of baptism and the Eucharist. The Discourse draws upon the previous tradition--especially Origen, St Methodius of Olympus, and, above all, St Athanasius' On the Incarnation...