Why purposely including specific keywords in articles, blogs etc. for SEO?

[Joao]

I understand for SEO purposes, articles, blogs, comments etc need to be written with the link to your website in the resource box. I also understand that specific keywords need to be written on all pages of your website so searchers for those keywords will quickly find your website. However, why is it necessary to put specific keywords in articles, blogs etc? Does the backlink to your website not suffice for SEO? Thanks in advance
Thank you all for your reply!

So if I understand correctly, the reason why keyswords in articles, blogs are important aside to keywords on your site: is because the combination of the backlink to your website on blogs, articles etc. + the keywords on blogs, articles etc. create more value (vote) for your website, which means it will rank higher.

So this is not to rank the article or blog itself higher, the keywords will only help the website. I can't imagine how to rank an article higher in the SERPS, since this is a one time written article. Unlike a website, you dont modify or work on an article after that.

Is there any way how to rank a specific article higher in the SERPS?