I clothe the heavens with blackness - With the dark clouds of a tempest - perhaps with an allusion to the remarkable clouds and tempests that encircled the brow of Sinai when he gave the law. Or possibly alluding to the thick darkness which he brought over the land of Egypt (Exodus 10:21; Grotius). In the previous verse, he had stated what he did on the earth, and referred to the exhibitions of his great power there. He here refers to the exhibition of his power in the sky; and the argument is, that he who had thus the power to spread darkness over the face of the sky, had power also to deliver his people.
I make sackcloth their covering - Alluding to the clouds. Sackcloth was a coarse and dark cloth which was usually worn as an emblem of mourning (see the note at Isaiah 3:24). The same image is used in Revelation 6:12 : ‘And I beheld when he had opened the sixth seal, and lo, there was a great earthquake; and the sun became black as sackcloth of hair.’ To say, therefore, that the heavens were clothed with sackcloth, is one of the most striking and impressive figures which can be conceived.