Isaiah 58:5

Is it such a fast that I have chosen? a day for a man to afflict his soul? is it to bow down his head as a bulrush, and to spread sackcloth and ashes under him? wilt thou call this a fast, and an acceptable day to the LORD?

Is it such a fast that I have chosen? A day 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 so far as it leads us to amend our ways (Isaiah 58:6).

(Is it) to bow down his head as a bulrush, and to spread sackcloth? - to affect the outward tokens, so as to "appear to men to fast" (Matthew 6:17; ; ).