The main purpose of using a content management system (CMS) in web development is to facilitate the creation, management, and modification of digital content. A CMS provides a user-friendly interface for non-technical users to update web pages without needing extensive coding knowledge. This can include features for editing text, uploading images, and managing permissions. CMS platforms also often come with plugins or modules for enhanced functionality, such as SEO tools and analytics, thereby streamlining the management of a website.