When you pray, do not stop praying until you have aroused some sort of feeling towards God in your heart. This can be reverence, or devotion, or thanksgiving, or praise, or humility and contrition, or trust and hope. Do this also when you begin reading during your devotions; do not stop reading until you have felt the truth that you have read. And if you pay attention to yourself, these two feelings, by warming you up, are capable of keeping you under their influence all day...
When something is out under the sun's rays for a long time, it gets very warm; the same thing will happen for you. By keeping yourself under the rays of remembrance of God and your feelings towards him, you will be warmed more and more with the unearthly warmth, and then you will become completely fiery, not just fiery, but ablaze.This is a glorious challenge to all of us. With faith, love, dedication, and our best efforts, we all can focus our attention continually upon our God. When we put our whole effort into this, we can feel the warmth of Him in our heart. It is this warmth that gives us the intensity and the desire to remain focused on God no matter what is happening around us. It is uplifting, hopeful, and comforting.
Pray, read the Scriptures, study the church fathers, attend church services regularly, and do all of these things with great sincerity and with your full attention. Then, you, as Saint Theophan advises, will feel the loving warmth of Christ our God in your heart.
Reference, The Spiritual Life, p 222-224