Ancient Jewish mystical practices laid the groundwork for many elements of modern synagogue worship, as revealed through a close examination of *Hekhalot Rabbati*, the seminal text of Merkavah mysticism from the first to third centuries C.E. This pseudepigraphical work, which describes mystical ascents through seven heavenly palaces, contains the earliest versions of prayers still central to Jewish liturgy today. Through comparative analysis of the text's hymns and prayers against established liturgical works, supported by interpretations from Scholem, Gruenwald, and other scholars of Jewish mysticism, clear lines of transmission emerge. Fundamental prayers of daily Jewish worship, particularly the *Kedushah*, originated within mystical circles before their adoption into formal liturgy. Three primary liturgical themes surface: direct textual parallels between mystical hymns and contemporary prayers including the *Bar'khu*, *Sh'ma*, and *Aleinu*; theurgical concepts emphasizing Israel's prayers affecting divine actions; and ritual elements such as the three-times-daily prayer cycle, the *minyan*, and the role of the *shaliah zibur*. As a crucial bridge between biblical sources and rabbinic liturgy, *Hekhalot Rabbati* challenges conventional views of Judaism as purely rationalistic, revealing the mystical foundations that continue to shape Jewish worship practices.