Possible Clues:

• Word with Agnus or Opus
• Word "of god"
• 'Agnus (Mass prayer) --'
• '-- gratia' ('by the grace of God')
• Agnus . . . - Lamb of God
• ___ gratia (by the grace of God)
• --- gratia
• Capo ___ capi (big boss, in 35-Across)
• Augustine's 'De civitate ___'
• Of the, in Venice