On Repeating Prayers when Thoughts Wander
When your mind does wander during prayer, bring it back. When it wanders again, bring it back again. Each and every time that you read a prayer while your thoughts are wandering (and consequently you read it without attention and feeling,) then do not fail to read it again. Even if your mind wanders several times in the same place, read it again and again until you read it all the way through with understanding and feeling. In this way, you will overcome this difficulty so that the next time, perhaps, it will not come up again, or if it does return, it will be weaker. This is how one must act when the mind wanders.
– Bishop Theophan the Recluse