Implicit in Heidegger's 1920-1921 Phenomenology of Religious Life is an account of religion as a radical transformation of the very structures of experience. This article seeks to apply that account to a classical Indian discourse on reality and the self, Chāndogya Upanis . ad chapter six. This classical source-text for two thousand years of Hindu theology advocates a new 'religious life' achieved through phenomenologically reorienting the very structures of cognition toward the broadest truths of reality, rather than the finite features of the world. The goal is to create a new form of primordial subjectivity with an altered relationship to phenomena, finitude, and the divine. The article proceeds in two parts: The first section brings out Heidegger's theory of religion through a reading of Heidegger's 1920 Phenomenology of Religious Life with the help of his lectures, On the Definition of Philosophy, from the previous year. The second section tries to demonstrate the value of integrating traditional textual/historical scholarship in the Chāndogya Upanis . ad with Heidegger's method. The juxtaposition aims to both (1) foreground the phenomenologically transformative goals of this influential Indian text, and (2) challenge Heidegger's scepticism about the religious value of metaphysical reflection.This article looks at what it means to enter a new 'religious life' by phenomenologically reorienting the very structures of experience toward the broadest truths of reality-that is, by shifting one's perspective so fundamentally that the world is experienced in terms of its universal features, rather than its finite, transient details. Heidegger's 1919-1921 lectures on 'The Phenomenology of Religious Life' described his vision of what the Christian experience can and should be. But they also contained a broader theory of religion, taking it to be a cultural form that alters the most basic patterns of our experience of the world in such a way that it reorients our sense of identity, values, and behaviour. Complimenting this, they also demonstrated a ground-breaking method of reading that seeks 'to penetrate therewith into the grounding phenomena of primordial [religious] life.' Here, we apply this to a classical Hindu text that aimed to create a new form of experience which alters one's relationship to phenomena, finitude, and the divine. 1 In the Chāndogya Upanis . ad, a 6th century text that shaped Hindu understandings of divinity for two millennia, a father asks his 'swollen-headed' son whether his teachers have passed on a special kind of truth that does not just fill the mind, but also transforms it: 1 The Upanis . ads are generally taken as introducing proto-philosophical ideas about metaphysics, identity, causality, and selfhood, that would later be refined in India's scholastic traditions. Texts, like the Chāndogya Upanis . ad, a c.7th century reflection on language and meaning, universalisation and essence, and finitude and immortality, highlights the uses of philosophical thinking as a spiritual exercise...