Some great snippets from Tertullian (c.160-220) found in today's Office of Readings in the Liturgy of the Hours:
"Prayer is an offering that belongs to God and is acceptable to him: it is the offering he has asked for, the offering he planned as his own."
"We must dedicate this offering with our whole heart, we must fatten it on faith, tend it by truth, keep it unblemished through innocence and clean through chastity, and crown it with love."
"Prayer cleanses from sin, drives away temptations, stamps out persecutions, comforts the fainthearted, gives new strength to the courageous, brings travelers safely home, calms the waves, confounds robbers, feeds the poor, overrules the rich, lifts up the fallen, supports those who are falling, sustains those who stand firm."
"What more need be said on the duty of prayer? Even the Lord himself prayed."