In this article – the first Bishop Kevin Dunn Memorial Lecture ‐ I argue that one of the most important resources available for Catholics seeking to understand or teach Trinitarian doctrine is the liturgy of the Mass. I suggest that the text of the liturgy (novus ordo) offers us three patterns of Trinitarian speech that we should emulate. The first ascribes equal glory to Father, Son and Spirit. The second pattern teaches us that the fundamental story of Christian faith is a Trinitarian one. The creation comes from the Father, through the Son and in the Spirit; salvation is a process of being incorporated into the Son by the Spirit so that we may be led to the Father. This narrative is seen particularly clearly in the new eucharistic prayers of the Roman rite. The third pattern is that of using such theological formulae“as one nature and three persons”. These formulae are used sparingly and in contexts which emphasize that the realities of which they speak remain mysterious ‐ and must be the subject of our worship if our understanding is to grow. In our thought, teaching and prayer we should be attentive to the relative priority that these liturgical patterns suggest.