8 But those “proud ones have hidden a trap for me;” they have sought to trip up my steps. And what have they done? “And have stretched out cords as traps.” What cords? The word is well known in holy Scripture, and elsewhere we find what “cords” signify. For “each one is holden with the cords of his sins,” says Scripture. And Esaias says openly, “Woe to them that draw sin like a long rope.” And why is it called a “cord”? Because every sinner who perseveres in his sins, adds sin to sin; and when he ought by accusing his sins to amend, by defending he doubles what by confession he might have removed, and often seeks to fortify himself by other sins, on account of the sins he has already committed....But these their sins they “spread” for the righteous, when they persuade them to do the evils which they themselves do.
Therefore he said, “they spread cords and traps;” that is, by their sins they desired to overthrow me. And where did they this? “Beside the paths have they laid a stumbling-block for me:” not in the paths, but, “beside the paths.” Your “paths” are the commandments of God. They have “laid stumbling-blocks beside the paths;” do not thou withdraw out of the paths, and you will not rush upon stumbling-blocks. Yet will I not that you should say, “God should prevent them from laying stumbling-blocks beside my paths, and then they would not lay them.” Nay, rather, God permitted them to “lay stumbling-blocks beside your paths,” that you should not leave the paths.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)