זוהר שמות — דף קיה ע”ב

One who engages in Torah in order to merit the World to Come is called "acquisition." One acquired by his Master forever, whose ear is pierced by the recitation of the Shema — fifty gates of Binah morning and evening — has no redemption through another in transmigration. The service of prayer is the slavery of six years: three opening and three closing blessings of the Amidah. The heads of the heavenly academy said to the Faithful Shepherd: both the supernal and lower Shekhinah spoke with you face to face in the Shema — yod is the sword's tip, vav its tongue, and the two hehs are its two edges on your lips.