To enable revision and to log revision message on saving a node in drupal 8 we can use setNewRevision() and setRevisionLogMessage(). Find the below code which uses entity save with revision.
Revisions in Drupal 8 comes as a part of core. Every time when you edit or create a content in Drupal 8 you will be provided with an option to create a of that content or page. This is helpful for the process of revert back to the older content.