Your content needs links to be able to rank. Google can only find your posts and pages when they’re linked to from somewhere on the web. In addition to that, internal links connect your content and give Google an idea of the structure of your website. They can establish hierarchy on your site, which enables you to give the most important pages and posts more link value than other, less valuable, pages. This means that the right internal linking strategy can boost your SEO!
Why are links important to Google?
Google crawls websites by following links, internal and external, using a bot: Google bot. This bot first enters the homepage of a website, starts to render the homepage and follows the first link. By following links Google determines what the relation is between certain pages, posts and other content. This way Google finds out which pages on your site are topically related.
In addition to understanding the relation between content, Google divides link value over all links on a website. Often, the homepage of a website has most link value because it has most backlinks. This link value will be spread over all the links found on that homepage. The link value that is passed to a following page will be divided over the links on that page, and so on.
If you understand this, you’ll understand that having lots of (internal) links to a page, will pass more link value to that page. Because Google deems a page with lots of valuable links more important, you’ll increase the chance of ranking for that page.
Read the full article: Internal linking for SEO: why and how • Yoast