John Gill Bible Commentary

Let their way be dark and slippery,.... In which they run before the angel, chasing and pursuing them; so that they know not where they are, at what they stumble, whither to flee, nor how to stand; the ways of wicked men are as darkness, they know not in what condition they are, and whither they are going; and utter darkness, even blackness of darkness, is reserved for them: but here it means a calamitous, uncomfortable, fickle, and unstable situation in this life; see Jer 23:11. The allusion is to some of the valleys in the land of Palestine, which were dark, and the roads in them very smooth and slippery, as travellers in those parts have observed (q); and let the angel of God persecute them; See Gill on Psa 35:5. (q) See Maundrell's Travel's, p. 7.