Prayer, as we understand it, consists of two parts, petition and thanksgiving. The categories listed by Paul (1 Timothy 2.1) all come down to these two elements. In our petitions, we lay before God our heart and our desire, asking Him, in His goodness, first for those things which seek only to serve His glory, and then for the things which are useful to us and which we need. In our thanksgiving, we acknowledge His benefits toward us and we confess them to His praise, thanking Him for everything as, overall, we give Him glory for all His blessings and ascribe them to His goodness. These two elements David includes in a single verse, speaking in the person of our Lord: “Call upon Me in the day of your need; I will deliver you and you will glorify Me” (Psalm 50.15). We should continually employ both of these things for our want and poverty are so great, our imperfection presses us so hard on every side and so burdens us that we must all, even the most godly, have cause, at every hour, to lament and sigh to God and to call upon Him in all humility.
From: Institutes of the Christian Religion by John Calvin; the French edition of 1541; translated by Robert White (Edinburgh: The Banner of Truth Trust, 2014), p. 534.