John Gill

I clothe the heavens with blackness,.... With gross and thick darkness; perhaps referring to the three days' darkness the Egyptians were in, Exo 10:12, or with thick and black clouds, as in tempestuous weather frequently; or by eclipses of the sun; there was an extraordinary instance of great darkness at the time of Christ's crucifixion, Mat 27:45. and I make sackcloth their covering; that being black, and used in times of mourning; the allusion may be to the tents of Kedar, which were covered with sackcloth, or such like black stuff. The fall of the Pagan empire, through the power of Christ and his Gospel, is signified by the sun becoming black as sackcloth of hair, Rev 6:12. Jarchi interprets this parabolically of the princes of the nations, when the Lord shall come to take vengeance upon them; as Kimchi does the sea, and the rivers, in the preceding verse, of the good things of the nations of the world, which they had in great abundance, and should be destroyed.