Albert Barnes Commentary Isaiah 58:8

"Then shall thy light break forth as the morning, and thy healing shall spring forth speedily; and thy righteousness shall go before thee; the glory of Jehovah shall by thy rearward." — Isaiah 58:8 (ASV)

Then shall thy light - (See the notes at Isaiah 44:7). The idea here is that if they were faithful in the discharge of their duty to God, he would bless them with abundant prosperity . The image is that such prosperity would come on the people like the spreading light of the morning.

And thine health - Lowth and Noyes render this, ‘And your wounds shall be speedily healed over.’ The authority on which Lowth relies is the version of Aquila as reported by Jerome, and the Chaldee. The Hebrew word used here (ארוּכה 'ărûkâh), means properly “a long bandage” (from ארך 'ârak—“to make long”), such as is applied by surgeons to heal a wound (compare the notes at Isaiah 1:6).

It is then used to denote the healing that is secured by the application of the bandage, and figuratively here means their restoration from all the calamities that had been inflicted on the nation. The word rendered ‘spring forth’ (from צמח tsâmach) properly relates to the manner in which plants germinate (compare the notes at Isaiah 42:9). Here the sense is that if they would return to God, they would be delivered from the calamities that their crimes had brought on them, and that peace and prosperity would again visit the nation.

And thy righteousness shall go before thee - Shall be your leader—as an army is conducted. The idea is that their conformity to the divine laws would serve the purpose of a leader to conduct them in the ways of peace, happiness, and prosperity.

The glory of the Lord - The allusion here is doubtless to the way in which the children of Israel came out of Egypt (see the notes at Isaiah 6:5).

Shall be thy rere-ward - Margin, ‘Shall gather you up.’ That is, shall bring up the rear (see the notes at Isaiah 52:12).