The Philokalia

by Nicodemus of the Holy Mountain

the Elder said to him: 'You have had a brief taste of stillness and inner work, and have experienced the sweetness that comes from them. This is what you should always be doing in your heart: whether eating or drinking, in company or outside your cell, or on a journey, repeat that prayer with a watchful mind and an undeflected intellect; also chant, and meditate on prayers and psalms. Even when carrying out needful tasks, do not let your intellect be idle but keep it meditating inwardly and praying. For in this way you can grasp the depths of divine Scripture and the power hidden in it, and give unceasing work to the intellect, thus fulfilling the apostolic command to 'Pray without ceasing' (1 Thess. 5:17). Pay strict attention to your heart and watch over it, so that it does not give admittance to thoughts that are evil or in any way vain and useless. Without interruption, whether asleep or awake, eating, drinking, or to company, let your heart inwardly and mentally at times be meditating on the psalms, at other times be repeating the prayer, 'Lord Jesus Christ, Son of God, have mercy upon me.' And when you chant, make sure that your mouth is not saying one thing while your mind is thinking about another.