The role of content writing for search engine optimization could be understood from the fact that all algorithms used by any of the search engine is based on the keywords related to theme of the website and use of that keyword within the content of the website. In order to emphasize a keyword, it is broadly used at different sections of a web page and website.
Your keywords and phrases need to be common in such a way that they must be in demand by very common reader and users of a website. And the keywords should be phrased within sentences that could be crawled by spiders of a search engine. Here comes the role of an experienced content writer to fit that keyword in right place in a write up at the beginning and end of a sentence with prominence.
Apart from that a keyword should be treated properly in Title, Meta and Alt tag of a web page. Thus proper placing of a keyword can bring a handsome placing for your corporate or e-commerce site on the SERP (Search Engine Result Page).
However, merely fetching words cannot bring you big results in term of search engine ranking what else you need to keep in mind that there should be some clarity in terms of language, grammar and writing style as well.