Keil & Delitzsch

Ashes are his bread (cf. Lam 3:16), inasmuch as he, a mourner, sits in ashes, and has thrown ashes all over himself, Job 2:8; Eze 27:30. The infected שׁקּוי has שׁקּוּ = שׁקּוּו for its principal form, instead of which it is שׁקּוּי in Hos 2:7. "That Thou hast lifted me up and cast me down" is to be understood according to Job 30:22. First of all God has taken away the firm ground from under his feet, then from aloft He has cast him to the ground - an emblem of the lot of Israel, which is removed from its fatherland and cast into exile, i.e., into a strange land. In that passage the days of his life are כּצל נטוּי, like a lengthened shadow, which grows longer and longer until it is entirely lost in darkness, Psa 109:23. Another figure follows: he there becomes like an (uprooted) plant which dries up.