One of the significant factor for your blog to be recognized is using keywords so your blog is search engine friendly. What I meant to say is, for your blog to be searchable it needs to be optimized and one way of doing that is using "keywords" and some even use keyword phrases so as not to saturate. In other words, if you are going to use it so many times also in your post it may appear that it is spammy and it could not be looking good for your readers and most especially in the search engine. When optimizing your blog it needs a balance of the "keywords" that you are going to use so it won't affect your ranking in the search engine results page.
I have read many articles and from experts that the number of keywords depends on the number of words you are writing in an article. Also Google does not like keywords to be used more than 2% in a given post. So if you are writing a 200 word article then you should not be repeatedly use your keyword more than 4 times. I usually use only three keywords for that given article.
Another thing is, spread out the keywords. Many have suggested that you use one each in a given paragraph. And to maximize your SEO (Search Engine Optimization) juice, place your keywords in the first sentence of your article and somewhere at the last part of your last paragraph. In this way, you have a better chance in ranking good in search engine results page. But again, you should know that keywords is just one of the factors that will influence your rankings. Hope you learn something about how important the keywords is.