The article analyses the document teotamachilizti, a sermon in a Nahuan language from colonial Guatemala. It concludes that the language is a Central Nahuan language closely related to "classical Nahuatl", but with some features of an Eastern Nahuan language closely related to Pipil Nawat. It is suggested that the document was written by an ecclesiastic who was schooled in Central Mexican Nahuatl, but who was adapting the sermon to a local audience who spoke an Eastern Nahuan vernacular.