“Why is it, you ask, that one can pray for so many years with a prayer book, and still not have prayer in his heart? I think the reason is that people only spend a little time lifting themselves up to God when they complete their prayer rule, and in other times, they do not remember God. For example, they finish their morning prayers, and think that their relation to God is fulfilled by them; then the whole day passes in work, and such a person does not attend to God.”
(St Theophan the Recluse,  ‘Homily on Prayer’)