This is from “Taking Hold of God” by Joel R. Beeke and Brian G. Najapfour… page 38.

(The) concept of piety includes attitudes and actions that are directed to the adoration of God.  Prayer is the principal and perpetucal exercise of faith and the chief element of piety…  Prayer shows God’s grace to the believer even as the believer offers praises to God and asks for His faithfulness.  Prayer expresses piety both privately and coporately.  Herman Selderhuis says that… the Psalms stress “prayer is not so much about moving God to a responsive action so much as it is given to bring a believer to greater confidence” in God.  This, in turn, promotes a lifestyle of authentic piety.  An increased piety requires prayer, for prayer diminishes self-love and multipies dependence on God.  Prayer unites God and man, not in substance, but in will and purpose.  Like the Lord’s Supper, prayer lifts the believer to Christ and renders glory to God.