Psalms 140:8

Grant not, O Lord, the desires of the wicked - That is, in the matter under consideration. Let them not accomplish their desire in my destruction. Let them not succeed in their designs against me. The prayer, however, "may" be used more generally. It is proper to pray that the desires of the wicked, as wicked people, may not be granted to them; that they may "not" be successful in their purposes. Success in such desires would be only an injury to themselves and to the world. It is proper to pray that the purposes of the wicked may be defeated, and that they may be led to abandon their designs and to seek better ends. For this, in fact, we always pray when we pray for their conversion.

Further not his wicked device - His purpose against me.

Lest they exalt themselves - Lest they attribute it to their own skill, wisdom, or valor, and lest they pride themselves on their success. To succeed in a righteous cause makes a man humble and grateful; in a bad cause, proud, and forgetful of God. The margin here is, "Let them not be exalted." The meaning is, that success would at the same time elate them in their own estimation, and increase their bad influence in the world. It is, on every account, a benevolent prayer that wicked people may "not" be successful in their plans of iniquity.