With the apostolic letter Traditionis custodes, issued motu proprio in July 2021, Pope Francis severely curtailed the circumstances in which the pre-conciliar form of the Roman Rite may be celebrated, reversing the position of his predecessor, Benedict XVI. For some so-called traditionalist commentators, this was an inappropriate restriction upon liturgical diversity. This article will review the development of the understanding of liturgical diversity and unity in the magisterium since the council, and explore how Francis’ restrictions restore the model for diversity developed out of Sacrosanctum Concilium. This article will then propose a theological reading where the tension between diversity and unity contribute to a liturgical demonstration of the catholicity of the church.