The meanings of texts

Today (december tenth, the last day of class) we discussed Derrida and his statement that "there is nothing outside the text" or something along those lines.  This was explained as saying that once an author has written something, they are then "dead" to the text and it is up to the reader to give it meaning.  While there can be importance in this view of literary works, I feel that it does not give the whole picture.

When we read a book, there is obviously some purpose behind the book.  Do we write simply for the sake of writing?  Or do we mean to show something through our words?  In writing this am I leaving it up to your interpretation that could have very little do with my original intent?  I would say that when something is written it has some inherent purpose, something that is trying to be conveyed.

If I write a letter wishing someone to get better quickly, my intent is to let them know I hope them a speedy recovery and nothing else that they might decide they'd like to have received more.  Likewise, if I were to write a book describing a healthier way to live, it is meant to be followed according to plan and not for someone to pick and choose what they want of it.

Picking and choosing from such a text may work to some extent in its own right; however, doing so diminishes the effectiveness of the intended outcome.  So is this applicable to philosophical texts as well?  I think it may be even more deeply ingrained in philosophical texts from their nature.  Finding truth and determining why things are the way they are, this needs clear statements and not random interpretations.  So even if the author is dead and we cannot know what they were intending, do we still not look and try to analyze what they meant by what they said?

My thought is that the text receives its meaning from the author and it is our job to determine what they intended and not to give it a new meaning that we deem appropriate.