Isaiah 58:5

This was not the type of fasting God approved (cf. Isaiah 1:11; Psalms 51:16-17; Luke 18:9-14). It consisted only in His people bowing their heads, not their hearts. Bowing the head like a reed expresses formal worship, like a reed automatically bending in response to wind. The people sat in sackcloth and ashes, but they did not really mourn over their disobedience to the Lord. They thought their outward fasting, bowing, dressing, and adorning were more important than their attitudes and behavior, though they probably did not realize it and certainly did not admit it (cf. James 1:27; James 4:8).

"When we worship because it is the popular thing to do, not because it is the right thing to do, then our worship becomes hypocritical." [Note: Wiersbe, p. 66.]