Here is a great quote on prayer from John Calvin’s Institutes III:XX:2. I have broken it up for easier reading.

Words fail to explain how necessary prayer is, and in how many ways the exercise of prayer is profitable. Surely, with good reason the Heavenly Father affirms that the only stronghold of safety is in calling upon his name.

By so doing we invoke the presence

             of his providence,

                       through which he watches over and guards our affairs, 

             and of his power

                       through which he sustains us, weak as we are and well nigh overcome

             and of his goodness,

                       through which he receives us, miserably burdened with sins, unto grace;

and in short, it is by prayer that we call him to reveal himself as wholly present to us.

Hence comes extraordinary peace and repose to our consciences. For having disclosed to the Lord the necessity that was pressing upon us, we even rest fully in the thought that none of our ills is hid from him who, we are convinced, has both the will and the power to take the best care of us.