There are 2 clues to be found here.
The first is the cross on the wall nearby the crypt of Abbot Suger.
"Freshly engraved, bearing the words: "Dieu Resistant in Pentiere".
Look at the foot the skeleton of Abbot Suger. If you use Eagle Vision, you will see a scrap of paper sitting there.
"We, the congregation of Dieu Resistant in Panetiere, had to appoint ourselves guardians over the Abbot's last will.
"We welcome the faithful in these dire times, exempt of God, exempt of justice.
"The Panetiere congregation shall lead the penitent to God's hidden house.
"In nomine patris, et filii, et spiritus santi, Amen."