Deceit is in the heart of them that imagine evil: but to the counsellors of peace is joy.

Wesley's Notes

12:20 Deceit - They whose hearts devise mischief shall be deceived in their hopes, and bring trouble upon themselves: but they who by good counsels labour to promote peace, shall reap the comfort of it themselves.

Jamieson-Fausset-Brown Bible Commentary

20. that imagine-or, "plan" (Pr 3:29). They design a deceitful course, to which, with all its evils and dangers to others and themselves, the happiness of peace-makers is opposed (compare Mt 5:9; Ro 12:18).

Matthew Henry's Concise Commentary

12:16. A foolish man is soon angry, and is hasty in expressing it; he is ever in trouble and running into mischief. It is kindness to ourselves to make light of injuries and affronts, instead of making the worst of them. 17. It is good for all to dread and detest the sin of lying, and to be governed by honesty. 18. Whisperings and evil surmises, like a sword, separate those that have been dear to each other. The tongue of the wise is health, making all whole. 19. If truth be spoken, it will hold good; whoever may be disobliged, still it will keep its ground. 20. Deceit and falsehood bring terrors and perplexities. But those who consult the peace and happiness of others have joy in their own minds. 21. If men are sincerely righteous, the righteous God has engaged that no evil shall happen to them. But they that delight in mischief shall have enough of it. 22. Make conscience of truth, not only in words, but in actions. 23. Foolish men proclaim to all the folly and emptiness of their minds. 24. Those who will not take pains in an honest calling, living by tricks and dishonesty, are paltry and beggarly. 25. Care, fear, and sorrow, upon the spirits, deprive men of vigour in what is to be done, or courage in what is to be borne. A good word from God, applied by faith, makes the heart glad. 26. The righteous is abundant; though not in this world's goods, yet in the graces and comforts of the Spirit, which are the true riches. Evil men vainly flatter themselves that their ways are not wrong. 27. The slothful man makes no good use of the advantages Providence puts in his way, and has no comfort in them. The substance of a diligent man, though not great, does good to him and his family. He sees that God gives it to him in answer to prayer. 28. The way of religion is a straight, plain way; it is the way of righteousness. There is not only life at the end, but life in the way; all true comfort.

Matthew Henry's Whole Bible Commentary

Verse 20

Note, 1. Those that devise mischief contrive, for the accomplishing of it, how to impose upon others; but it will prove, in the end, that they deceive themselves. Those that imagine evil, under colour of friendship, have their hearts full of this and the other advantage and satisfaction which they shall gain by it, but it is all a cheat. Let them imagine it ever so artfully, deceivers will be deceived. 2. Those that consult the good of their neighbours, that study the things which make for peace and give peaceable advice, promote healing attempts and contrive healing methods, and, according as their sphere is, further the public welfare, will have not only the credit, but the comfort of it. They will have joy and success, perhaps beyond their expectation. Blessed are the peace-makers.