Once you have blogged for a while, you will have enough content that you would want users to read. With internal linking, you can send new readers to check out your older relevant posts.
Internal linking is a great way to develop a contextual relationship between your new and old posts. It also allows you to pass relevant link juice to your older articles.
WordPress makes it easy to search for your old posts right inside the post editor. Simply select the text that you want to link and then click on the link button.