Sufi interpretation of the Qurʾān—often termed taʾwīl or esoteric exegesis—seeks to uncover the inner spiritual meanings of the Islamic scripture beyond its literal text. This paper revises and expands the discussion on Qurʾānic mysticism, situating it within both Sufi and Shiʿi traditions, and examines the epistemological foundations that enable such interpretations. Drawing on contemporary scholarship and classical sources, we explore how Sufi and Shiʿi thinkers conceptualize the Qurʾān as a multi-layered revelation with ẓāhir (outward) and bāṭin (inward) meanings. We analyze definitions of taʾwīl, historical debates over its legitimacy, and the methods by which mystics claim to “return” the verses to their divine origin. Special attention is given to the role of ʿilm ḥuḍūrī (knowledge by presence), maʿrifat al-nafs (self-knowledge), fiṭra (innate disposition), and tawḥīd (divine unity) as philosophical and mystical epistemologies underpinning esoteric hermeneutics. Balancing these insights, the study highlights that genuine mystical exegesis in Islam does not negate the exoteric meaning or the Sharīʿa; rather, it integrates outward and inward, reason and intuition. Through engagement with Sufi commentaries and Shiʿi mystical teachings—from early Sufi tafsīrs to modern seminarians—we demonstrate that mystical Qurʾān interpretation is a disciplined quest for deeper understanding of revelation, aiming at personal transformation and direct communion with the Ultimate Reality. The paper concludes that far from being a subjective or innovative reading, authentic mystical exegesis is grounded in the Islamic tradition’s view of the Qurʾān as a “love-letter” from God to man, inviting the seeker to unveil divine secrets through purification, love, and inner realization.