The following thoughts are distilled from the writings of John Bunyan, but expressed in my words (sparing you the interpretation of his Old English):
How rare it is for our heart and mouth to go into prayer together! When your words ask for anything, does your heart truly desire it, hungering after it? The power of prayer comes from the longings of our heart, not from our choice of words.
While men are praying with words, sighs, and groans, God is searching the heart to see what the Spirit finds there. It is only through the Spirit’s influence on our hearts and His expression of our hearts’ desires that we can pray according to God’s will (Romans 8:26-27).
In prayer it is better to have a heart without words than words without a heart.