In yesterday’s post, “The evil of sin works for good to the godly,” Thomas Watson addressed the good that comes out of sins that are committed against the believer. But then he also adds a second benefit that arises from sin: the benefit that is derived from our own sin against others (be sure to read his third to last paragraph carefully so that you don’t misconstrue his intent).
The sense of their own sinfullness will be overruled for the good of the godly. Thus our own sins shall work for good. This must be understood warily, when I say the sins of the godly work for good — not that there is the least good in sin. Sin is like poison, which corrupts the blood, infects the heart, and, without a sovereign antidote, brings death. Such is the venomous nature of sin, it is deadly and damning. Sin is worse than hell, but yet God, by His mighty over ruling power, makes sin in the issue turn to the good of His people. Hence that golden saying of Augustine, “God would never permit evil, if He could not bring good out of evil.” The feeling of sinfullness in the saints works for good several ways.
(i.) Sin makes them weary of this life. That sin is in the godly is sad, but that it is a burden is good. St. Paul’s afflictions (pardon the expression) were but a play to him, in comparison of his sin. He rejoiced in tribulation (2 Cor. vii. 4). But how did this bird of paradise weep and bemoan himself under his sins! “Who shall deliver me from the body of this death?” (Rom. vii. 24). A believer carries his sins as a prisoner his shackles; oh, how does he long for the day of release! This sense of sin is good.
(ii.) This in being of corruption makes the saints prize Christ more. He that feels his sin, as a sick man feels his sickness, how welcome is Christ the physician to him! He that feels himself stung with sin, how precious is the brazen serpent to him! When Paul had cried out of a body of death, how thankful was he for Christ! “Il thank God through Jesus Christ our Lord” (Rom. vii. 25). Christ’s blood saves from sin, and is the sacred ointment which kids this quicksilver.
(iii.) This sense of sin works for good, as it is an occasion of putting the soul upon six especial duties:
(a) It puts the soul upon self searching. A child of God being conscious of sin, takes the candle and lantern of the Word, and searches into his heart. He desires to know the worst of himself; as a man who is diseased in body, desires to know the worst of his disease. Though our joy lies in the knowledge of our graces, yet there is some benefit in the knowledge of our corruptions. Therefore Job prays, “Make me to know my transgressions” (Job xiii. 23). It is good to know our sins, that we may not flatter ourselves, or take our condition to be better than it is. It is good to find out our sins, lest they find us out.
(b) The inherence of sin puts a child of God upon self-abasing. Sin is left in a godly man, as a cancer in the breast, or a hunch upon the back, to keep him from being proud. Gravel and dirt are good to ballast a ship, and keep it from overturning; the sense of sin helps to ballast the soul, that it be not overturned with vain glory. We read of the “spots of God’s children” (Deut. xxxii. 5). When a godly man beholds his face in the glass of Scripture, and sees the spots of infidelity and hypocrisy, this makes the plumes of pride fall; they are humbling spots. It is a good use that may be made even of our sins, when they occasion low thoughts of ourselves. Better is that sin which humbles me, than that duty which makes me proud. Holy Bradford uttered these words of himself, “I am a painted hypocrite”; and Hooper said, “Lord, I am hell, and Thou art heaven.”
(c) Sin puts a child of God on self-judging; he passes a sentence upon himself. ” I am more brutish than any man” (Prov. xxx. 2). It is dangerous to judge others, but it is good to judge ourselves. “If we would judge ourselves, we should riot be judged” (I Cor. xi. 31). When a man has judged himself, Satan is put out of office. When he lays anything to a saint’s charge, he is able to retort and say, “It is true, Satan, I am guilty of these sins; but I have judged myself already for them; and having condemned myself in the lower court of conscience, God will acquit me in the upper court of heaven.”
(d) Sin puts a child of God upon self-conflicting. Spiritual self conflicts with carnal self. “The spirit lusts against the flesh” (Gal. v. 17). Our life is a wayfaring life, and a war-faring life. There is a duel fought every day between the two seeds. A believer will not let sin have peaceable possession. If he cannot keep sin out, he will keep sin under; though he cannot quite overcome, yet he is overcoming. “To him that is overcoming” (Rev. ii. 7).
(e) Sin puts a child of God upon self-observing. He knows sin is a bosom traitor, therefore he carefully observes himself. A subtle heart needs a watchful eye. The heart is like a castle that is in danger every hour to be assaulted; this makes a child of God to be always a sentinel, and keep a guard about his heart. A believer has a strict eye over himself, lest he fall in to any scandalous enormity, and so open a sluice to let all his comfort run out.
(f) Sin puts the soul upon self-reforming. A child of God does not only find out sin, but drives out sin. One foot he sets upon the neck of his sins, and the other foot he “turns to God’s testimonies” (Psalm cxix. 59). Thus the sins of the godly work for good. God makes the saints’ maladies their medicines.
But let none abuse this doctrine. I do not say that sin works for good to an impenitent person. No, it works for his damnation, but it works for good to them that love God; and for you that are godly, I know you will not draw a wrong conclusion from this, either to make light of sin, or to make bold with sin. If you should do so, God wilt make it cost you dear. Remember David. He ventured presumptuously on sin, and what did he get? He lost his peace, he felt the terrors of the Almighty in his soul, though he had all helps to cheerfullness. He was a king; he had skill in music; yet nothing could administer comfort to him: he complains of his “broken bones” (Psalm li. 8). And though he did at last come out of that dark cloud, yet some divines are of opinion that he never recovered his full joy to his dying day. If any of God’s people should be tampering with sin, because God can turn it to good; though the Lord does not damn them, He may send them to hell in this life. He may put them into such bitter agonies and soul convulsions, as may fill them full of horror, and make them draw nigh to despair. Let this be a flaming sword to keep them from coming near the forbidden tree.
And thus have I shown, that both the best things and the worst things, by the overruling hand of the great God, do work together for the good of the saints.
Again, I say, think not lightly of sin.
Words of Grace 
Self reforming. I say this sounds like a hopeless cause that drove Paul to declare: “Who shall save me from this body of death?”
If you read enough of Watson and other Puritans you know that they understand well the work of God to change the heart of men — we work, but God is the one that produces the change (Phil. 2:12-13). But they were also unafraid to say what many are more reticent to say today, namely, “mortify (kill!) your sin,” and “put to death the deeds of the flesh” (e.g., Rom. 8:13; Col. 3:5). It is this that Watson is emphasizing (note the sentence after he mentions self-reforming: “A child of God does not only find out sin, but drives out sin”). He is emphasizing that when one recognizes his sin and sees what his sin has done to others, it leads him to work all the harder to mortify that sin.