What Cranmer did was not primarily to write new doctrine. It was to compress the whole apparatus of medieval Latin worship, spread across a breviary, a missal, a manual and a pontifical, into one book in English that a parish priest could hold in one hand and a congregation could follow.
The 1549 book was the first, conservative in tone and designed to be usable by clergy who had said mass all their lives. The 1552 revision went considerably further: the words of administration at communion were changed so that they no longer implied any change in the bread, the vestments went, the altar became a table. His own eucharistic theology had moved, and the second book is where it settled.
The prose is the part that outlived the theology. Cranmer wrote for the ear, in balanced pairs and long falling cadences, and phrases from him are still in general circulation among people who could not name him: to have and to hold, from this day forward; ashes to ashes, dust to dust; the peace of God, which passeth all understanding. He was translating and adapting rather than inventing, drawing on Latin collects, on Lutheran orders and on the reformed breviary of Cardinal Quiñones, and the achievement is one of compression and rhythm rather than of originality. It is one of the very few works of committee-adjacent liturgy anywhere that is also a monument of a national literature.