With my whole heart I cry; answer me, O LORD!
I will keep your statutes. (Psalm 119:145)

If the cry to the Lord uttered by those who pray is made with the sound of the bodily voice without the heart being turned to God, who can doubt that it is made in vain? But if it comes from the heart, even if the bodily voice is silent, it can be concealed from everybody else but not from God.
Therefore when we pray – weather aloud as required or silently – to God, our cry must come from the heart. –St. Augustine  (Augustine Day by Day, Catholic Book Publishing Co. 1986, Page 71)