Read the story in the link. How do you explain this behavior?

The soviet secret police accused Fr Walter Ciszek of being a Vatican spy.  He was sentenced to twenty-three years of hard labor in Siberia.  In his book He Leadeth Me: An extraordinary Testament of Faith, Fr. Ciszek tells of prisoners who would deprive their bodies of needed sleep to attend a secret Mass before the monitoring bell would ring.  Huddled in slush and mud, risking severe punishment if they were discovered, they cherished their encounter with Christ there.  How do you explain this behavior?