Keywords are the main factors that is primarily considered every time one writes about a certain topic or issue. Why? Because keywords help people locate what they are seeking for. Now if the keywords you used for a blogsite isn't that popular, then your blog will also not gain popularity.
It is of course a fact that we blog because we want to share, we want to interact with other people who have the same interest as we do. Now, how could we share if no one actually knows where to locate you and how?
Keywords or key phrases are the ones that helps you for your blog to gain popularity and for your target readers to reach you. For one to get across his/her intended message, he/she must give importance to keywords.