The feast that gives Tavener's work its title commemorates a specific reported event: sometime in the early tenth century, at the Blachernae Palace church in Constantinople, worshippers including the visionary Andrew the Fool for Christ reported seeing the Theotokos, the Mother of God, appear above the congregation and spread her veil, her maphorion, over the people gathered there, a gesture Orthodox tradition reads as a sign of her continuing protection over the faithful. The Orthodox Church commemorates the vision annually on October 1 as the Feast of the Protecting Veil, or Pokrov.
Tavener sets no words at all in the piece named for that feast; The Protecting Veil is purely instrumental, cello against strings, which means the connection to the Blachernae vision and to the eight subsequent episodes of Mary's life the piece's eight sections trace has to be carried entirely by the music itself, by the cello's high, sustained, voice-like lines against the surrounding string texture, rather than by any sung or spoken text a listener could follow along with directly.
Tavener himself described his broader compositional aim, across this piece and much of his later religious output, as trying "to make a lyrical icon in sound," treating a musical work the way Orthodox tradition treats a painted icon: not as a literal illustration of an event, but as a devotional object meant to open a window onto something beyond itself, which for The Protecting Veil is specifically the Orthodox veneration of Mary as a continuous, still-active protective presence rather than as a figure confined to a single completed historical episode.