Emacs is very hard to characterize. It is usually thought of as an extensible text editor. It is actually much, much, more. It can be used as an email client, an appointment book, or a file manager.
Major modes customize the methods of editing particular types of files.
This allows keywords and special constructs within each mode to be drawn differently, typically in different colors. The feedback from such highlighting prevents many common typos. This also prevents the common typo of forgetting to end blocks. Sure, there are other editors which can accomplish these tasks for particular languages or applications. It is also extensible.