If your website isn't mobile friendly right now, the SEO future is about to get pretty bleak.
Google has officially started the process of rolling out "mobile-first indexing" but, of course, only for those websites that adhere to the best practices.
In the past, Google's crawling, indexing, and ranking systems used the desktop version of a page's content, but mobile-first indexing now means that the mobile version of a page will be used instead.
Google indicated that it is notifying those websites being migrated to mobile-first indexing through the Search Console interface and clearly noted that being indexed this way provides no ranking advantage.
Site owners will likely see significantly increased crawl rate from the "Smartphone" Googlebot as a result of the change. Additionally, Google will show the mobile version of pages not just in Search results but also within Google cached pages.