In Isaiah's day, Israelites were saying to God:
“Keep to yourself, do not come near me, for I am too holy for you.”
The Holy Bible : English Standard Version. (Wheaton: Standard Bible Society, 2001), Is 65:5.
They were following a form of religion that made them feel good, and made them feel holy. In fact they felt so holy that they didn't need God to come near them. The language is reminiscent of when God gave his law in Exodus 20, and the people wanted God to speak to Moses rather than themselves, because they were afraid. Here in Isaiah however, the people don't want God to speak to them because they are too holy for him! In other words, they do not feel the need to submit to God's words, because they are okay. Today, many people act the same way, when they neglect to read scripture because,
"I know it all"
"I've read the bible before"
"I don't get much out of reading the bible"
"I just focus on my relationship with God instead"
In contrast to this, God wants us to have an attitude that trembles at his word:
But this is the one to whom I will look: he who is humble and contrite in spirit and trembles at my word.
The Holy Bible : English Standard Version. (Wheaton: Standard Bible Society, 2001), Is 66:2.
The Israelites were still making sacrifices, yet because they would not listen to God's word, their sacrifices were disgusting to God:
“He who slaughters an ox is like one who kills a man; he who sacrifices a lamb, like one who breaks a dog’s neck; he who presents a grain offering, like one who offers pig’s blood; he who makes a memorial offering of frankincense, like one who blesses an idol. These have chosen their own ways, and their soul delights in their abominations; 4 I also will choose harsh treatment for them and bring their fears upon them, because when I called, no one answered, when I spoke, they did not listen; but they did what was evil in my eyes and chose that in which I did not delight.”
The Holy Bible : English Standard Version. (Wheaton: Standard Bible Society, 2001), Is 66:3-4.
This means that it is possible to be involved in religious ceremony, worship meetings etc. and yet because of a failure to listen to God's word (the Bible), our actions can be disgusting to God.
Recently, I've been studying Charismatic and Pentecostal movements of the last century, and something that has concerned me, is that so many so-called movements have placed more emphasis on worship music, and less on the ministry of the word.
As Don Carson says,
In every generation, what ultimately distinguishes the true from the false among God’s people, the blessed from the cursed, is faithfulness or unfaithfulness to the Word of God.
D. A. Carson, For the Love of God : A Daily Companion for Discovering the Riches of God's Word. Volume 2 (Wheaton, Ill.: Crossway Books, 1998), 25.