Tallis and Byrd's Cantiones sacrae (1575). A Sacred Argument, Hardback/Jeremy L. (Customer) Smith

What did Tallis and Byrd mean to convey by their use of the word "argument" in their title, Cantiones, quae ab argumento sacrae vocantur? Publisher: Boydell & Brewer Ltd Author(s): Jeremy L. (Customer) Smith Illustration(s): 26 mus exx, 34 b/w illus. Number of pages: 284 Publication date: 2023 Dimensions: 164 x 242 x 24 Cover type: Hardback