I. The Hebrew prophet's deliverance here is not in condemnation or disparagement of all fasting. The people of his day were in the habit, it appears, of denying themselves food, and assuming postures of mourning and humiliation as an offering to the Almighty, and an appeal to Him for His recognition and regard, whilethey were living, and persisted in living, unrighteously and unlovingly. Ever and anon, they would set apart a time in which to make themselves generally uncomfortable, by going without their meals, and spreading sackcloth and ashes over themselves, as an act towards Jehovah, and a call upon Him for His favour, whiletheir lives were rank with injustice and selfishness. This was what their religious teacher inveighed against so sharply: the idea that to stop once and again in a course of bad conduct, and lie in the dust, with bent heads, and empty, unfed mouths, was a ceremony acceptable to God, and would suffice to atone in a measure for their habitual covetousness and cruelty.
II. While Isaiah is denouncing the superstition of his countrymen in thinking to compound for their transgressions by bodily abstinences and austerities, he is led, it would appear, to consider the practice of fasting with outward signs of humiliation and mourning, and to ask the question, "Is it ever what the Lord desires and demands? "And the answer of the prophet's soul is, "No." Men will and must fast if heavily oppressed with grief, and they may and should fast if it will help them at all in the effort to rise above false passion, and subordinate the lower nature to the higher. But to fast and lie in the dust, as an offering to God, as an exercise toward Him, for Him to look upon and be attracted by, is altogether vain and worthless. The one true repentance is to turn from the ways of sin into the ways of righteousness. The fear of the Lord is to depart from evil, and if a man be departing from evil he need not trouble about any further confession or repentance, except in so far as his own heart should compel him. In departing from evil he is fasting the fast which God chooses, which is not to afflict his soul with abstinence for a day, and to bow down his head as a bulrush, but to "loosen the bands of wickedness," and to "deal his bread to the hungry."
S. A. Tipple, Christian World Pulpit,vol. xv., p. 200.
References: Isaiah 58:4. J. G. Rogers, Christian World Pulpit,vol. iii., p. 145.Isaiah 58:5. F. W. Farrar, Ibid.,vol. xxxi., p. 129.