Prayer Skills-Redeeming Prayers
“You will direct their heart, You will cause Your ear to attend (Psalms 10:17).” This means that when they pray with proper intention of the heart, You will “cause Your ear to attend,” and fulfill their wishes. Similarly, “You have given him his heart’s desire, and the request of his lips You have not withholden, Selah (Psalms 21:3).” This means that a mere “request of the lips,” without Kavanah may not impede the fulfillment of the duty to pray, your “hearts desire” will not be granted unless you have prayed with proper intention at least once. But this one prayer would elevate all the delayed prayers which are then enveloped in it.
This is indicated in the verse, “A prayer of the afflicted when he is faint (Psalms 102:1),” which the Zohar interprets as enveloping, namely, that all prayers are enwrapped into the prayer of the afflicted, thus reaching their destination along with it. The same holds true in regard to Kavanah.
That is what is meant by, “You have not withholden, Selah,” although no benefit is derived a present from the prayer which is a mere utterance of the lips, it may ultimately be beneficial, as attested by the word Selah, which means “forever.”
The same may be said in regard to the Rambam’s ruling that the absence of Kavanah is a hindrance to prayer. He means to say that Kavanah hinders or defers the prayer’s elevation and acceptance to the point that its requests are fulfilled until one prays at least once with intention.
Prayer with proper Kavanah is a biblical Commandment; prayer with out it is only a rabbinic duty. (Lishon Chassidim, Tefillah #51)