‘But you, O Daniel, shut up the words and seal the book, even to the time of the end. Many will run to and fro, and knowledge will be increased.'
The idea is not that the book is made so that it cannot be read, only that its final fulfilment awaits the time of the end. The book can now be shut up and sealed because it is completed. Then an official sealed copy can be preserved for official consultation while other copies are made available to all. Then the end will reveal its truth. The sealing was for authentication and identification.
‘Many will run to and fro, and knowledge will be increased.' For the meaning of the verb compare Job 1:7 b, ‘going too and fro on the earth'. Amos 8:12 depicts men as running to and fro to seek the word of YHWH but as being unable to find it. So the picture here is that because men ignore this book they will run to and fro around the world, seeking the word of YHWH, gaining a kind of knowledge, but never able to find the truth, because they do not turn to this book or to the Scriptures.