A. Martin Heidegger (H), son of a Catholic sexton, began his higher education as a Jesuit, majored in theology at U of Freiburg, and did his Ph.D. on Duns Scotus, whose notion of univocity of being was of course encountered by H, whose thesis title was "Duns Scotus' Doctrine of Categories and Meaning," with emphasis on time, number, and logical basis of such. His earlier qualifying dissertation was "The Doctrine of Judgment in Psychologism." This is the arc of H: Catholicism, questioning vis a vis psychologism, and subsequent focus on number (univocity of being in time, per logic qua epistemology).
C. In child-speak, Martin Heidegger was a Catholic boy who later majored in philosophy.
A. The one subject H swore off of: "Geist" qua Spirit. This indicates a bifurcation between God, I Am, and "Dasein," or (human) "being there." H focused on the latter. In the philosophy of religion, the Deific is capitalized. In secular philosophy, the non-Deific is often capitalized, as a type of deification or reification: e.g., Kant's Transcendental, Sartre's Transcendental, etc. So H's "Being" = secular existing. H reframed the Seinsfrage ("question of being"), which was "answered" by Duns Scotus in his univocity of being formulation (~ "I Am the One" as applying to both God and God's Man). H's rationale for moving from Spirit, I Am, to there-existing, parallels and reflects his declination from Spirit, I Am. H posits a fallacy, termed the "metaphysics of presence," in which all people who claim Spirit, I Am, I and the Father are One, etc., are simply pre-Kantian Noumenalists (although H did not use this term). H assumed or posited that anyone (e.g., Christ Jesus) who claimed Gnosis or Knowing of Spirit was deceived. (This of course does not imply that H was self-deceived). Instead, H develops an ontology of circumstance, of what the more spirited Karl Jaspers termed the "surround," essentially saving the Immanence. H's teacher, Edmund Husserl, who considered himself a free-thinking Christian, catagorized H's position as anthropologism, i.e., not obtaining God-awareness per phenomenological epoche and eidetic reduction...in other words, misunderstanding or failing to assimilate Husserl's method.
C. Heidegger believed Being arose of circumstances (existence precedes being). Some earlier philosophers, such as Duns Scotus and Saint Thomas Aquinas, believed that Being reflected Man in God's Image and likeness.
A. H did not complete his grand opus "Being and Time," and "later H" had a "turning" into a more mystical approach to how one may happen upon disclosure or "unconcealment," which was a theme of the Zeitgeist (cf Joan Miro's paintings). Central to this existential notion of arising and subsiding events was "light" of the mystical poet...imh (non-snarky) opinion, a key existential happening in H's life was Johanna Arendt. In Christian-speak, this (poetic) event = some poets who write of the "Unknown God," particularly germane to H, who delved into Greek word-structure (much as early Nietzsche). A modern philosopher who was imho successfully completed the early H project is Peter Sloterdijk, whose popular work "You Must Change Your Life" reflects the Rodin-to-Rilke advice reprised in the book's title. Imho Sloterdijk is succeeding in restoring Duns Scotus' univocity of being per a more personal focus per a more Husserlian eidetic appreciation.
C. The end.