the gift of discernment is neither earthly nor of little account, but is, rather, a very great boon of divine grace. And if a monk does not do his utmost to acquire it and if he does not have a clear knowledge of the spirits rising up against him he will surely stray
Cassian establishes discernment as a supreme divine gift, arguing that without it the monk cannot distinguish demonic from divine promptings and will inevitably fall into spiritual error.
, Conferences, 426thesis