58:3-12 A fast is a day to afflict the soul; if it does not express true sorrow for sin, and does not promote the putting away of sin, it is not a fast. These professors had shown sorrow on stated or occasioned fasts. But they indulged pride, covetousness, and malignant passions. To be liberal and merciful is more acceptable to God than mere fasting, which, without them, is vain and hypocritical. Many who seem humble in God's house, are hard at home, and harass their families. But no man's faith justifies, which does not work by love. Yet persons, families, neighbourhoods, churches, or nations, show repentance and sorrow for sin, by keeping a fast sincerely, and, from right motives, repenting, and doing good works. The heavy yoke of sin and oppression must be removed. As sin and sorrow dry the bones and weaken the strongest human constitution; so the duties of kindness and charity strengthen and refresh both body and mind. Those who do justly and love mercy, shall have the comfort, even in this world. Good works will bring the blessing of God, provided they are done from love to God and man, and wrought in the soul by the Holy Spirit.
5. for a man to afflict his soul—The pain felt by abstinence is not the end to be sought, as if it were meritorious; it is of value only in so far as it leads us to amend our ways (Isa 58:6, 7).
bow … head … sackcloth—to affect the outward tokens, so as to "appear to men to fast" (Mt 6:17, 18; 1Ki 21:27; Es 4:3).