It is hard enough to enter into a sustained mood.
How much more difficult to accompany the words of the prayer book, ascending and descending as they do.
So that for instance we recite the Shmoneh Esrei with the consciousness of standing directly before God with no intermediary, then immediately afterward, in the Nefilat Apayim, we descend radically from divinity into created reality.
This is the nature of the entire prayer service: it moves from one extreme to the other, ascending and descending-which makes extremely difficult demands on a person's psyche.
A person's thoughts tend to be random and easily distracted, and can quickly shift from the holy to the profane.
We must work hard to keep our minds focused.
We must struggle with all our might.
This battle to maintain proper concentration has no clear ending.
If a person's only goal were to recite the words as written, he could succeed within a certain amount of time.
But struggling with the prayer experience, plumbing the meaning of word after word and sentence after sentence, is a neverending process.
Sometimes a person may apply himself fruitlessly–even if he applies himself repeatedly, his efforts may be in vain.
Our tradition refers to prayer as a time of battle.
In this battle, as in any other, one may lose.
Nevertheless, even when one has gained nothing, if one determines that next time one will pray with intensity, if one expresses that commitment repeatedly and believes that such a goal is attainable, then it truly is within one's reach.
When a person determinedly focuses on the words of prayer, he may be sure that one day something within him will burst into flame.
Even if he must repeat some passage in the prayer book a thousand times, he will reach the point where the words resonate with him and he recites them as an expression of his own feelings.
This method of serving God was taught by the Baal Shem Tov, and he illustrated it with a homiletic reading of God's command to Noah:
"Make a shining stone for the ark."
The word: "ark" in Hebrew–teva–can also mean "word."
A person must work on a word of prayer even when it is like a lifeless stone, until it begins to gleam and becomes like a glass through which divinity shines.
And how does one do so?
The verse continues: "Come, you and your entire household, into the teva".
A person comes and puts all of his being–his thoughts and feelings, his memories and dreams–into a word of prayer.
Its denotation and connotation.
Thus does he proceed, word after word and sentence after sentence.
–Rabbi Adin Steinsaltz
From "Prayer" in The Thirteen Petalled Rose (new edition) by Rabbi Adin Steinsaltz