Jamieson, Fausset and Brown on Isaiah 45:8

8. Drop--namely, the fertilizing rain (Psa 65:12).

skies--clouds; lower than the "heavens."

righteousness--that is, the dews of the Holy Spirit, whereby "righteousness" shall "spring up." (See latter end of the verse).

earth--figuratively for the hearts of men on it, opened for receiving the truth by the Holy Ghost (Ac 16:14).

them--the earth and the heavens. Horsley prefers: "Let the earth open, and let salvation and justice grow forth; let it bring them forth together; I the Lord have created him" (Is 45:13). Maurer translates, "Let all kinds of salvation (prosperity) be fruitful" (Psa 72:3, 6, 7). The revival of religion after the return from Babylon suggests to the prophet the diffusion of Messiah's Gospel, especially in days still future; hence the elevation of the language to a pitch above what is applicable to the state of religion after the return.