Breaking into the book business requires the author to be a little savvy not only for the writing part but for the business part as well.
Truth is most writers aren't very business savvy. They would prefer to just write and leave the business part to someone who enjoys that sort of thing....well, I do anyway.
These days, authors are required to get out there and promote, promote, promote. Gone are the days where the publisher will set up a marketing plan....unless you have already established yourself as a best selling author.
Anyway, before I lose my train of thought, sometimes we don't want to search out the publisher but prefer to have an agent do that sort of thing for us....
If you want to learn more about finding a literary agent that fits you and your work, check out Nathan Bransford blog to help you out.