React is a tool used to build web frontends. It’s used by Facebook, Dropbox, Instagram, Whatsapp, Khan Academy and many other giants. It basically makes frontend developers insanely productive.
React is one of many strong frontend tools and it will not last forever. React itself is a good teacher - by becoming good at React, a coder will develop a few transferable skills.
React can also be a stepping stone on the way to a strong cross-platform mobile development skill set. Once React has been mastered, getting into ReactNative or Ionic is not terribly difficult. And once any serious frontend toolset has been learned it’s not hard to transfer those skills to another toolset. For example Vue and Angular are quite popular already.
Take a look at this to see how React compares to the most popular web frameworks and libraries around: