“To attain a facility and dexterity of language in prayer, and put thy meaning into apt and decent expressions, is easy; but to get thy heart broken for sin, while thou art confessing it; melted with free grace while thou art blessings God for it; to be really ashamed and humbled through the apprehensions of God’s infinite holiness, and to keep thy heart in this frame, not only in, but after duty, will surely cost thee some groans and pains of soul. To repress the outward acts of sin, and compose the external part of thy life in a laudable manner, is no great matter; even carnal persons, by the force of common principles, can do this: but to kill the root of corruption within, to set and keep up the holy government over thy thoughts, to have all things lie straight and orderly in the heart, this is not easy…God rejects all duties (how glorious soever in other respects) which are offered him without the heart. He that performs duty without heart, that is heedlessly, is no more accepted with God than he that performs it with a double heart, that is, hypocritically.”
John Flavel, Keeping the Heart: How to Maintain Your Love for God (Fearn, Rosshire: Christian Focus Publications, 2012), 33–34.