Heart-work is hard work indeed.

'It is the hardest work. 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 thyself before the Lord, and tie up thy loose and vain thoughts to a constant and serious attendance upon him; this will cost thee something. 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 though art confessing it; melted with free grace while thou art blessing 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 an holy government over thy thoughts, to have all things lie straight and orderly in the heart, this is not easy.'  - John Flavel, Keeping the Heart, p19–20

When jokes are terrible

Commenting on the 9th commandment, "You shall not be a false witness against your neighbour." [Ex. 20:16], Calvin says: "Indeed, this precept even extends to forbidding us to affect a fawning politeness barbed with bitter taunts under the guise of joking. Some do this who crave praise for their witticisms, to others' shame and grief, because they sometimes grievously wound their brothers with this sort of impudence. [...] For it is absurd to think that God hates the disease of evilspeaking in the tongue, but does not disapprove of evil intent in the heart." (Calvin, Institutes, II. viii. section 48.)