You use keywords because people wants sometimes what answer's but they what keywords, ex: flower, which is used to be in plants is its keyword.
Keywords are the most important aspect of SEO work is that since keywords are what people look for when they plug terms into a search engine. Keywords always plays an important role in that. Keywords and key phrases are the principal mechanisms by which the search engine will select your site, so it is essential that the correct keywords are used and that they are located to best advantage.