The vision of all; i.e. "the entire vision"—all that Isaiah has put before them in verses 1-8. As the words of a book that is sealed; rather, the words of a letter (marginal rendering) or writing. Written documents were often sealed up to secure secrecy, the sealing being done in various ways.
When the writing was on a clay tablet, it was often enclosed in a clay envelope, so that the document could not be read till the outer clay covering was broken. Rolls of papyrus or parchment were secured differently.
One that is learned; i.e. "one that can read writing," which the ordinary Jew could not do, any more than the ordinary European in the Middle Ages. Neither the learned nor the unlearned Jews would be able to understand Isaiah's prophecy, so as to realize and accept its literal truth.
They were devoid of spiritual discernment. Even the rulers were but "blind loaders of the blind."