Complex sentence: The Bishopric had warned Saunière about his selling of masses, and had sent him two written warnings in May 1901, these written warnings were repeated in June 1903 and August 1904.
Split into simpler sentences: The Bishopric had warned Saunière about his selling of masses, and had sent him two written warnings in May 1901. These written warnings were repeated in June 1903 and August 1904.