The aim of the present work is to investigate the philosopher Martin Heidegger's motivations to formulate his fundamental ontology between 1920 and 1930, when the young thinker dedicated himself to the writings about the factual life of the first Christians, initiating his phenomenological hermeneutic project that culminated in the publication of his acclaimed work Sein und Zeit. Heidegger perceived in primitive Christianity something that pervaded the dogmatic question, bringing with it the relation between facticity and care that caused the Christian to undergo a transformation in his way of being. This transformation would result in what Heidegger called "authentic life. This path traced by Heidegger from the study of the phenomenology of religious life resulted in a reformulation of traditional metaphysics taking the theme of being into a new approach, where existence ceases to be transcendental and becomes hermeneutic.
