Blogs position your site as a relevant source of information to search engine queries. The more informative and valuable content you publish, the better your chances are at ranking high on the search engine results pages (SERPs).
Here are a few other ways that blogs impact SEO and rankings:
Improving click-through rate (CTR): As you rank higher in search engines, more people will find your pages and land on your site. Your CTR will improve over time as people find your blog naturally.
Growing your index: Your index is a complete list of all the pages on your site and how they connect. More pages on your site (and connections between them) shows Google that your site is a relevant, authoritative source.
Earning more backlinks: Backlinks are links from outside sources that lead to your page. Google rewards websites with more backlinks, so it should be a goal to write authoritative content that people want to link to and share.