Isaiah's words, particularly in chapter 58, aren't altogether different from Jesus' words to the Pharisees in the New Testament.  The Israelites were hyprocrites – they went to the temple and followed all of the rituals, but their daily living was not marked by the same zeal with which they boasted of their religious fervor.  They were stuck in religious routine, which is really just a form of hypocrisy because they weren't truly worshiping the Lord.  How do we know?  Isaiah draws attention to the way the Israelites were fasting.  The type of fasting that God desires is with humility.  We should be humbling ourselves before Him and before others with hearts for service.  This was not the case with the Israelites.  Before we point fingers, though, we need to ask ourselves if we're simply performing our religious routines so we can be noticed and so we can put a check on our list.  God is not interested in such weak devotion to Him.  He seeks a heart of humility that surrenders itself and its desires to Him.  It's only then that we can kill hypocrisy.