An heart that deviseth wicked imaginations, {h} feet that be swift in running to mischief,

(h) Meaning, the raging affections, which carry a man away in such sort that he cannot tell what he does.

Wesley's Notes

6:18 Deviseth - He whose practice it is to contrive wickedness. Swift - Such as greedily execute their wicked designs.

Matthew Henry's Concise Commentary

6:12-19 If the slothful are to be condemned, who do nothing, much more those that do all the ill they can. Observe how such a man is described. He says and does every thing artfully, and with design. His ruin shall come without warning, and without relief. Here is a list of things hateful to God. Those sins are in a special manner provoking to God, which are hurtful to the comfort of human life. These things which God hates, we must hate in ourselves; it is nothing to hate them in others. Let us shun all such practices, and watch and pray against them; and avoid, with marked disapproval, all who are guilty of them, whatever may be their rank.