Who leave the paths of uprightness,.... Or "righteousness", or the "right [and plain] ways" ; which the light of nature and the law of God, and especially the Gospel of Christ, direct to; and in which they have been trained up, having had a religious education; for it supposes them to have been externally in these ways, since they are said to leave them; for though persons do not easily and ordinarily leave the ways they have been brought up in, yet sometimes they do; and there are instances of it, and such generally are the worst of men;to walk in the ways of darkness: sin, ignorance, and infidelity; in which they that walk know not where they are, nor whither they are a going, and which must be very uncomfortable as well as dangerous; in which only works of darkness are done, and which lead to blackness of darkness, the darkness of hell; a miserable choice, a sad change this!
So Schultens renders it, "ways of horrid darkness".