The {h} wicked shall be a ransom for the righteous, and the transgressor for the upright.

(h) God will cause that to fall on their own heads, which they intended against the just by delivering the just, and putting the wicked in their places.

Wesley's Notes

21:18 A ransom - The wicked shall be brought into those troubles, which were designed by wicked men for the righteous: thus Haman was a ransom for Mordecai.

Jamieson-Fausset-Brown Bible Commentary

18. (Compare Pr 11:8). By suffering what they had devised for the righteous, or brought on them, the wicked became their ransom, in the usual sense of substitutes (compare Jos 7:26; Es 7:9).

Matthew Henry's Concise Commentary

21:9. It is best to shun bitter contention by pouring out the heart before God. For by prudence and patience, with constant prayer, the cross may be removed. 10. The evil desires of a wicked man's heart, lead to baseness in his conduct. 11. The simple may be made wise by punishments on the wicked, and by instructions to those who are willing to be taught. 12. Good men envy not the prosperity of evil-doers; they see there is a curse on them. 13. Such as oppress the poor by beating down wages, such as will not relieve according to their ability those in distress, and those in authority who neglect to do justice, stop their ears at the cry of the poor. But doubtless care is to be used in the exercise of charity. 14. If money can conquer the fury of the passions, shall reason, the fear of God, and the command of Christ, be too weak to bridle them? 15. There is true pleasure only in the practice of religion. 16. Of all wanderers in the ways of sin, those are in the most dangerous condition who turn aside into the ways of darkness. Yet there is hope even for them in the all-sufficient Saviour; but let them flee to him without delay. 17. A life of worldly pleasure brings ruin on men. 18. The righteous is often delivered out of trouble, and the wicked comes in his stead, and so seems as a ransom for him. 19. Unbridled passions spoil the comfort of all relations. 20. The plenty obtained by prudence, industry, and frugality, is desirable. But the foolish misspend what they have upon their lusts. 21. True repentance and faith will lead him that relies on the mercy of God in Christ, to follow after righteousness and mercy in his own conduct. 22. Those that have wisdom, often do great things, even against those confident of their strength. 23. It is our great concern to keep our souls from being entangled and disquieted. 24. Pride and haughtiness make men passionate; such continually deal in wrath, as if it were their trade to be angry. 25,26. Here is the misery of the slothful; their hands refuse to labour in an honest calling, by which they might get an honest livelihood; yet their hearts cease not to covet riches, pleasures, and honours, which cannot be obtained without labour. But the righteous and industrious have their desires satisfied. 27. When holiness is pretended, but wickedness intended, that especially is an abomination. 28. The doom of a false witness is certain. 29. A wicked man bids defiance to the terrors of the law and the rebukes of Providence. But a good man asks, What does God require of me? 30,31. Means are to be used, but, after all, our safety and salvation are only of the Lord. In our spiritual warfare we must arm ourselves with the whole armour of God; but our strength must be in the Lord, and in the power of his might.