Our soul is an eye from the Eye, sight from the Sight, light from the Light. But now, since our fall into sin, our eye, our soul, is diseased through sins.
Take the cataract off your eye, and you will see the spiritual Sun, the everlasting Eye, ten thousand times brighter than the material sun.
How often it happens in life that a man has one thing in his heart and another upon his lips, and wears two faces at one and the same time!
It is thus also during prayer, before God Himself, Who knows the secrets of the heart; a man also frequently wears two faces, saying one thing and having another in his heart and thoughts.
If, which happens still oftener, when saying a prayer, although he understands it and thinks about it, he does not sympathise in his heart with that which he is saying—being dead, and thus throwing the words to the air—then he deceives himself if he believes that he can please God by such a prayer.
This is strange, sinful duplicity! It is a bitter fruit and evidence of our fall into sin. It seems habitual to our heart to lie in prayer and in our intercourse with other men. The heart is a pillar of falsehood. “All men are liars” (Psalm cxvi:10).
The Christian must make use of every means in order to eradicate every falsehood from his heart, and to implant pure truth within it.
We must begin with prayer, as with a matter in which truth is indispensable before everything, in accordance with the Lord’s own words: “Worship Him in spirit and in truth” (John 4:24). Speak the truth from your heart (Psalm 15:2).
When we have learnt to speak the truth from our heart during prayer, we shall not allow ourselves to lie in our everyday life: sincere, true prayer, having cleansed our heart from falsehood, will protect it against falsehood in our relations with other men in worldly matters.
How can we teach ourselves to speak the truth from our heart during prayer? We must bring every word of the prayer down to our heart, lay it to heart, feel its truth in our heart, be convinced of all our need of that for which we ask God in prayer, or of the need of hearty gratitude for His great and innumerable benefits to us, and of most heartfelt praise for His great, most wise works in His creation.
John of Kronstadt (1829-1908; Russian Orthodox): My Life in Christ.