Keywords in your copy are one of the most important ways to get visitors to your site from the search engines. Just getting the visitors to your site won’t do you any good if they leave right away because your copy was optimized for the search engines, but not your human visitors.
Karon Thackston has written a good article published on businessknowhow.com. She talks about how to use keywords in your text without making them sound mechanical, like they were stuffed into the content.