For he stretcheth out his hand against God - The hand is stretched out for battle. It wields the spear or the sword against an enemy. The idea here is, that the wicked man makes God an adversary. He does not contend with his fellow-man, with fate, with the elements, with evil angels, but with God. His opponent is an Almighty Being, and he cannot prevail against him; compare the notes at Isaiah 27:4.
And strengtheneth himself - As an army does that throws up a rampart, or constructs a fortification. The whole image here is taken from the practice of war; and the sense is, that a wicked man is really making war on the Almighty, and that in that war he must be vanquished; compare Job 9:4.