These verses continue to discuss Joseph Smith. He will receive a book that is sealed. This verse is easy to confuse with the sealed portion that Joseph will later be told not to translate. At this point in the story of the coming forth, the entirety of the Book of Mormon is sealed by the inability of anyone to read it. Nevertheless, there will come a time when it will be translated, and then they “shall be read upon the house tops.” The message will be declared.
When it says that he would not deliver the book, that phrase clearly does not mean the meaning nor words of the book. That is the point of its having been written. Rather, this is an admonition not to deliver the plates. The verses following these two will discuss who may and who may not see the plates. Therefore, this injunction is that the plates shall not be delivered up.
There is still content on the plates which remains sealed, or which remains untranslated and untransmitted. That will come forth in even later days. The only hints we have about that content is that it will contain prophecies concerning the end of time. Perhaps they are prophecies that will be best understood only after they are fulfilled, and the seal will be broken to show how the events fit into the prophecies. For now, we do not know, because they remain sealed.