This paper proposes a corpus-linguistic approach to Jesuit missionary Luys de Valdivia’s 1606 Sermón en Lengua de Chile [Sermon in the Language of Chile]. It enquires into the importance, potential and limitations this text presents in shaping our understanding of sixteenth-century Mapudungun. It also surveys the historical and linguistic context of the Sermones and their author, highlighting the overlap between the processes of language documentation and evangelisation. Throughout, we spotlight a new resource for mining early textual witnesses for the Mapuche tongue: the Corpus of Historical Mapudungun. We examine a number of structural features of the corpus and its construction, going on to exemplify their use in a series of lexical, morphological and phonological case studies related to Valdivia’s work. We conclude by calling on the academic and non- academic communities to use the freely-available corpus materials and tools in order to promote a better understanding of the language, whilst at the same time enjoying and propagating it.