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, Isa 58:7).
bow ... head ... sackcloth - to affect the outward tokens, so as to “appear to men to fast” (Mat 6:17, Mat 6:18; 1Ki 21:27; Est 4:3).