Google loves website activity
Blogging shows that your website is fresh and current, and you are actively working and care about engaging with your customers. A fresh and active website shows the website is getting regular attention and the information is up-to-date and accurate.
Blog content helps google find keywords
The more content your website has, the more google has to work with to find you. With enough content, google can leverage the content on your website in finding keywords in their algorithms. The more content you have the more keywords google can find, and the more success your likely to have in getting traffic to your site.
SEO favors original content
There is a lot of content, and if your content is original, that makes it easier for Google to find you.