Complex sentence: The Blessed Virgin appeared to him to give him comfort and showed him another daily offering that he might do: to pray every day 7 decades of Hail Mary's meditating between each decade on one of the seven joys that she had lived in her life.
Split into simpler sentences: The Blessed Virgin appeared to him to give him comfort and showed him another daily offering that he might do. She told him to pray every day 7 decades of Hail Mary's meditating between each decade on one of the seven joys that she had lived in her life.