On Prayer - St. John of Kronstadt

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 payers hurriedly and without feeling:  "I had rather speak five words with my understanding than ten thousand words in an unknown tongue." (1)

But it would, of course, have been very well had we been able to say those ten thousand words in prayer with due understanding and feeling.  The Lord does not forsake those who labor for Him and who stand long before Him; for with what measure they mete, He will measure to them again, and He will reward them for the abundance of the sincere words of their prayer by sending into their souls a corresponding abundance of spiritual light, warmth, peace, and joy.  It is well to pray long and continually; but "All men cannot receive this saying, save they to whom it is given."(2)  it is better for those who are not capable of long prayers to say short prayers, but with a fervent spirit.

(1) 1 Corinthians 14:19
(2) St. matthew 19:11,12