Prayer is the bellows of the affections; it blows up holy desires and ardours of soul. Prayer has power with God. ‘Command me’ (Isaiah 14:11). Prayer is a key which unlocks the treasury of God’s mercy. Prayer keeps the heart open to God—and shut to sin. Prayer assuages the swellings of lust. It was Luther’s counsel to a friend, when he perceived a temptation begin to arise, to betake himself to prayer. Prayer is the Christian’s gun, which he discharges against his enemies. Prayer is the sovereign medicine of the soul. Prayer sanctifies every mercy (1 Tim. 4:5). Prayer is the dispeller of sorrow—by venting the grief it eases the heart. When Hannah had prayed, ‘she went away, and was no more sad’ (1 Sam. 1:18).

—Thomas Watson
All Things for Good, 20.