The present investigation approaches the First Letter of Peter from the question about the keys of discernment in the ethical discourse. As an introduction, a diagnosis is presented on the use of the letter in different theological disciplines. Methodologically, the discourse is approached by applying a rhetorical analysis in order to discover indications of the author’s strategy and, later, a theological analysis with the objective of systemati-zing what is exposed about the action of the Spirit in the believer. The results of the research help to identify clues for scrutiny in three areas: in relation to oneself, in social relations and in domestic relations. The study concludes with the updating of these keys as a new contribution of First Peter to the discipline of spiritual theology.