Once only Chassidim and Sefardim wore Rabbeinu Tam Tefillin, and Chabad Chassidim seldom wore them before age 18—a custom that the Rebbe overturned in 1966 with a landmark Sicha that called on every Jewish man from any background to begin wearing Rabbeinu Tam Tefillin starting from Bar Mitzvah. This two-part series explores the factors that contributed to this shift and its modern implications, through letters and Sichos.

Part I: The Halachic and Kabbalistic implications of Rabbeinu Tam Tefillin; The Rebbe's answers to individuals who asked to start wearing RT before marriage; The Rebbe grapples with the custom and builds toward a fundamental change.