“Heart-work is hard work, indeed. To shuffle over religious duties with a loose and heedless spirit will cost no great pains, but to set yourself before the Lord, and tie up your loose and vain thoughts to a constant and serious attendance upon Him, will cost you something. To attain a facility and dexterity of language in prayer and put your meaning into apt and decent expressions is easy; but to get your heart broken for sin while you are confessing it and melted with free grace while you are blessing God for it, to be really ashamed and humbled through the apprehensions of God’s infinite holiness, and to keep your heart in this frame not only in, but after duty will surely cost you some groans and travailing pain of soul. To repress outward acts of sin and compose the external part of your life in a laudable and comely 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 a holy government over your thoughts, to have all things lie straight and orderly in the heart, this is not easy.”
John Flavel, Keeping the Heart (SDG, 1998), 9f.