The Art of Divine Contentment: An Exposition of Philippians 4:11 by Thomas Watson. Excerpt 82

Watson, near the close of his book, sets forth some rules for becoming contented:

Rule 4. Keep a clear conscience. Contentment is the manna that is laid up in the ark of a good conscience: O take heed of indulging any sin! it is as natural for guilt to breed disquiet, as for putrid matter to breed vermin. Sin lies as Jonah in the ship, it raiseth a tempest. If dust or motes be gotten into the eye, they make the eye water, and cause a soreness in it; if the eye be clear, then it is free from that soreness; if sin be gotten into the conscience, which is as the eye of the soul, then grief and disquiet breed there; but keep the eye of conscience clear, and all is well. What Solomon saith of a good stomach, I may say of a good conscience, “to the hungry soul every bitter thing is sweet:” (Pr. 27. 7) so to a good conscience every bitter thing is sweet; it can pick contentment out of the cross. A good conscience turns the waters of Marah into wine. Would you have a quiet heart? Get a smiling conscience. I wonder not to hear Paul say he was in every state content, when he could make that triumph, “I have lived in all good conscience to this day.” When once a man’s reckonings are clear, it must needs let in abundance of contentment into the heart. 
Good conscience can suck contentment out of the bitterest drug, under slanders; “our rejoicing is this, the testimony of our conscience.” (2 Cor. 1. 12) In case of imprisonment, Paul had his prison songs, and could play the sweet lessons of contentment, when his feet were in the stocks. (Ac. 16. 25) Augustine calls it “the paradise of a good conscience;” and if it be so, then in prison we may be in paradise. When the times are troublesome, a good conscience makes a calm. If conscience be clear, what though the days be cloudy? is it not a contentment to have a friend always by to speak a good word for us? Such a friend is conscience.
A good conscience, as David’s harp, drives away the evil spirit of discontent. When thoughts begin to arise, and the heart is disquieted, conscience saith to a man, as the king did to Nehemiah, “why is thy countenance sad?” so saith conscience, hast not thou the seed of God in thee? art not thou an heir of the promise? hast not thou a treasure that thou canst never be plundered of? why is thy countenance sad? O keep conscience clear, and you shall never want contentment! For a man to keep the pipes of his body, the veins and arteries, free from colds and obstructions, is the best way to maintain health: so, to keep conscience clear, and to preserve it from the obstructions of guilt, is the best way to maintain contentment. First, conscience is pure, and then peaceable.
 
Thomas Watson lived from 1620-1686, in England. He wrote several books which survive. This blog, thank God, has posted excerpts from his The Art of Divine Contentment: An Exposition of Philippians 4:11, over a number of weeks, on Sundays.

My source for the text is here, and I thank the Christian Classics Ethereal Library for making this text (and many others) available. The previous excerpt is here.