 The development of Swedish liturgy was, in part, thanks to Olavus Petri, which is sometimes regarded as his most important work.His Swedish Mass, 1531 remained in use, with only slight modifications, until the twentieth century.The Swedish Mass draws from a number of different sources, though Luther’s "Formulae Missae" is apparent in regards to the Eucharistic structure This included revising the calendar along similar lines as those in Germany.