How might meditation be helpful for a patient with obsessive compulsive disorder?  

Negative habits: compulsions and other unwanted behaviors. Unwanted behaviors are part of a reinforcing pattern in which a trigger activates an urge, which then compels an action, which usually produces an immediate pleasant outcome followed by a later feeling of stressful self-criticism, judgment,...

Stepping outside of identifying with thoughts via meditation, mindfulness, prayerful state, artistic absorption, etc, creates distancing, which is the key first step to be a bit more free from the autocracy of obsessions and the need to compulsively attempt to reduce the accompanying anxiety.