The West formulated the principle of constant prayer in a more flexible way so that it could also be proposed to those who do not lead a monastic life. St. Augustine teaches that the essence of prayer is desire. If the desire for God is constant, so also is prayer, but if there is no interior desire, then you can howl as much as you want — to God you are mute.
Now, this secret desire for God, a work of memory, of need for the infinite, of nostalgia for God, can remain alive, even when one has other things to do: “Praying for a long time is not the same thing as kneeling or folding your hands for a long time. In consists rather in awakening a constant and devout impulse of the heart toward him whom we invoke.”
Jesus himself gave us the example of unceasing prayer. Of him, it is said that he prayed during the day, in the evening, early in the morning, and sometimes he passed the whole night in prayer. Prayer was the connecting thread of his whole life.
But Christ’s example tells us something else important. We are deceiving ourselves if we think that we can pray always, make prayer a kind of respiration of the soul in the midst of daily activity, if we do not set aside fixed times for prayer, when we are free from every other preoccupation.
On that note, from Teresa Polk (Blog by the Sea), “a collection of thoughts on how to pray silently in a noisy church.”