During prayer there sometimes occur moments of deadly darkness and spiritual anguish arising from unbelief of the heart (for unbelief is darkness). Do not let your heart fail you at such moments, but remember that if the Divine light has been cut off from you, it always shines in all its splendour and greatness in God Himself, in God’s Church, in heaven and on earth, and in the material world in which “His eternal power also and divinity” are visible. Do not think that truth has failed, because truth is God Himself, and everything that exists has its foundation and reason in Him.
Only your own weak, sinful and darkened heart can fail in the truth, for it cannot always bear the strength of the light of truth, and is not always capable of containing its purity, but only if it is being, or has been, purified from its sins, as the first cause of spiritual darkness. The proof of this you may find in yourself. When the light of faith or God’s truth dwells in your heart, only then is it tranquil, firm, strong, and living; but when this is cut off, then your heart becomes uneasy, weak as a reed shaken by the wind, and lifeless. Do not pay any attention to this darkness of Satan.
Drive it away from your heart by making the sign of the life-giving Cross! When praying, keep to the rule that it is better to say five words from the depth of your heart than ten thousand words with your tongue only. When you observe that your heart is cold and prays unwillingly, stop praying and warm your heart by vividly representing to yourself either your own wickedness, your spiritual poverty, misery, and blindness, or the great benefits which God bestows every moment upon you and all mankind, especially upon Christians, and then pray slowly and fervently. If you have not time to say all the prayers, it does not matter, and you will receive incomparably greater benefit from praying fervently and not hurriedly than if you had said all your prayers hurriedly and without feeling: “I had rather speak five words with my understanding … than ten thousand words in a tongue.”
As after having unworthily communicated, so also after having prayed unworthily and coldly, our soul feels equally ill at ease. This means that God does not enter our heart, being offended at its unbelief and coldness, and allows the evil spirit to nestle in our hearts, in order to make us feel the difference between His own presence and its yoke. Sometimes during prayer you feel a kind of estrangement from God, and despair.
Do not be carried away by such a feeling; it proceeds from the Devil. Say in your heart: “I despair not of salvation, reprobate as I am; and emboldened by Thine immeasurable compassion, I come unto Thee. If there is any hope of salvation for me, if Thy loving mercy can overcome the multitude of my transgressions, be Thou my Saviour.” When praying with people, we sometimes have to pierce through with our prayer as if it were the hardest wall – human souls, hardened and petrified by earthly passions – to penetrate the Egyptian darkness, the darkness of passions and worldly attachments. This is why it is sometimes difficult to pray. The simpler the people one prays with, the easier it is. –
Fr. John of Kronstadt, a Russian Orthodox saint, as quoted in A Treasury of Russian Spirituality by G.P. Fedotov