In my understanding REST is just a name for when HTTP (and in particular its verbs GET, PUT, POST, DELETE, HEAD) are used to operate on data (resources) by using URL paths, headers and data. The objective is something similar to the good old "remote procedure call" concept where computers can invoke actions on remote computers. There used to be complicated technologies like CORBA and plain RMI to aid computers in being able to communicate with each others.
Modern often means simple. It should be easy to operate or resources via a web API and REST is often the answer. Use the HTTP technology which is already there and embrace it and create technologies around it. KISS principle is king, as opposed to inventing a proprietary complex and useless own method of data communication.
REST is a light-weight implementation of Web Service, which evolved from other distributed architecture solutions, such as CORBA, RMI, COM/DCOM, SOAP, SOA with XML. Here is a brief report on the history of Web Service: http://bit.ly/1jkySqU
But instead of XML, it employs data format of JSON to reduce the data size and every time it only returns a portion of the data, instead of return a complete set of data according to XML schema. This saves a lot of time for fast communication, especially if the application data set is small and simple, such as chatting.
But one interesting question is: Axis has one mode using RPC call, which is pretty fast and flexible based on SOAP using object serialization. But it's no longer popular now. Do you know why? There is a little trick of the object serializing when passing the parameters, though. But it can do RPC call so easily than the key/value pairs of JSON.
REST doesn't have to be JSON, it's agnostic with regard to the serialization format. JSON is just a popular format but I've seen XML and YAML REST apis.
Modern often means simple. It should be easy to operate or resources via a web API and REST is often the answer. Use the HTTP technology which is already there and embrace it and create technologies around it. KISS principle is king, as opposed to inventing a proprietary complex and useless own method of data communication.