Google's newest update landed yesterday on April 21st. It should take up to a week or a little more for this update to take full effects. The objective of the update is to remove the pages that are not mobile ready from the top organic ranking positions. This update favors those pages that are mobile friendly meaning they are easy to read, navigate, quick loading, and have buttons that are easy to use and not hard to click upon. Not all pages must be mobile ready but only those pages that are mobile ready will be seen in the top search results. If you have no pages in your site that are mobile ready as soon as you update the site to become mobile friendly, Google will add you back to the results quickly. There will be no need of waiting for monthly updates for site re-inclusion.
Mobile optimization is the process of ensuring that visitors who access your site from mobile devices have an experience optimized for the device.