From SuspireWiki

A period of 40 nights of reflection, prayer and fasting meant to be a reflection of the 40 nights Longinus was cursed to wander mad with starvation, cursed with hallucinations. It is said to be when Longinus found his true path, as the Dark Prophet. In truth, Sanctified only spend the very last week fasting and break the fast with the Feast of Longinus.