Finnish in the Medieval Period

Finland was added to Catholic Sweden in the Middle Ages, prior to this, Finnish was an oral language. After this, the language of larger-scale business was Middle Low German, the language of administration was Swedish and religious activities were in Latin, leaving few possibilities for Finnish-speakers to use their mother tongue in everyday situations.
The first known example of written Finnish was found in a German travel journal dating back to c.1450: Mÿnna tachton gernast spuho somen gelen Emÿna daÿda
Modern Finnish: "Minä tahdon kernaasti puhua suomen kieltä, [mutta] en minä taida";
English: "I willingly want to speak Finnish, [but] I can't").
According to the travel journal, a Finnish bishop, was behind the above quotation.