For they intended evil against thee - literally, “They stretched out evil.” The idea seems to be derived from “stretching out” or laying snares, nets, or gins, for the purpose of taking wild beasts. That is, they formed a plan or purpose to bring evil upon God and his cause: as the hunter or fowler forms a purpose or plan to take wild beasts or fowls. It is not merely a purpose in the head, as our word “intended” would seem to imply; it supposes that arrangements had been entered into, or that a scheme had been formed to injure the cause of God - that is, through the person referred to in the psalm. The purposes of wicked men against religion are usually much more than a mere “intention.” The intention is accompanied with a scheme or plan in their own mind by which the act may be accomplished. The evil here referred to was that of resisting or overpowering him who was engaged in the cause of God, or whom God had appointed to administer his laws.
They imagined a mischievous device - They thought, or they purposed. The word rendered “mischievous device” מזמה mezimmâh - means properly “counsel, purpose; then prudence, sagacity;” then, in a bad sense, “machination, device, trick.” Gesenius, Lexicon. Proverbs 12:2; Proverbs 14:17; Proverbs 24:8.
Which they are not able to perform - literally, “they could not;” that is, they had not the power to accomplish it, or to carry out their purpose. Their purpose was plain; their guilt was therefore clear; but they were prevented from executing their design. Many such designs are kept from being carried into execution for the want of power. If all the devices and the desires of the wicked were accomplished, righteousness would soon cease in the earth, religion and virtue would come to an end, and even God would cease to occupy the throne.