"Be stunned and amazed, blind yourselves and be sightless; be drunk, but not from wine, stagger, but not from beer. The Lord has brought over you a deep sleep: He has sealed your eyes (the prophets); he has covered your heads (the seers)." NIV translation
Isaiah now begins to describe the fact that his people were dazed and confused by the word of God much like someone that has been drinking alcohol. He goes on to explain that it is God that has kept them from seeing and understanding the prophecy that has been delivered.
"For you this whole vision is nothing but words sealed in a scroll. And if you give the scroll to someone who can read, and say, 'Read this, please,' they will answer, 'I can't; it is sealed.' Or if you give the scroll to someone who cannot read, and say, 'Read this, please,' they will answer, 'I don't know how to read.'" NIV translation
Isaiah goes on to describe the fact that the people didn't believe that man could understand the word of God. They may have had the scroll but they did not have the power to read and understand it.
This same type of thing happens today even among Christians as there are many who say that we cannot understand the Book of Revelation. Those who say such a thing are just as dazed and confused as the people of Isaiah's day. The fact of the matter is that, through the power of the Holy Spirit, we CAN read and understand the things of God.
"The Lord says: 'These people come near to me with their mouth and honor me with their lips, but their hearts are far from me. Their worship of me is based on merely human rules they have been taught.'" NIV translation
You can almost hear the distaste that God has for religion as He says that Israel's worship was just religion. They just went through the motions of rituals without having any real relationship with God. We are reminded that God is the same today and there is no amount of religious activity that can gain you a right relationship with Him.