There are three kinds of attention that can be brought to vocal prayer: one which attends to the words, lest we say them wrong; another which attends to the sense of the words; and a third which attends to the end of the prayer, namely, God, and to the thing we are praying for. This last kind of attention is most necessary, and even uneducated people are capable of it. Moreover, this attention, whereby the mind is fixed on God, is sometimes so strong that the mind forgets everything else.
–Saint Thomas Aquinas (1225-1274)