When the wicked spring as the grass - When they grow up as plants do; when they seem to flourish and prosper. Compare Psalms 90:5-6; Psalms 37:2, Psalms 37:35, Psalms 37:38. The word “grass” here refers to the vegetable creation generally, embracing plants and flowers of all kinds.
And when all the workers of iniquity do flourish - As plants and flowers do. They are like vigorous plants; not like the stunted and dry shrubs of the desert.
It is that they shall be destroyed for ever - The meaning here is, not that the design of their being thus made to flourish is that they should be destroyed, or that they are made to flourish for that purpose, but that such “will be” the result. They will not be made happy in another world by their prosperous and prospered wickedness here, as if God approved of their course; but the end will be that they will be destroyed forever. The design of the psalmist seems to be to turn the mind from the idea that mere external prosperity is necessarily connected with happiness; or that one who is prospered in this life is on that account safe. There is another world, and “there” ample justice will be done to all. See Psalms 73:16-20.