Final answer:
The first and most important application of the ARPANET was email, enabling communication among researchers and the eventual expansion that led to the modern Internet and World Wide Web.
Step-by-step explanation:
One of the first and most important applications of the ARPANET was email. The Advanced Research Projects Agency Network (ARPANET) was initiated as an effort to connect government and research institutions for exchanging information. Email quickly became a vital tool for personal and professional communication among researchers and users of the network, although commercial and political communications were not initially allowed. ARPANET evolved into a broader network, that, after standardization of communication protocols, eventually gave rise to the Internet and later the World Wide Web, revolutionizing the way information was shared and paving the way for evolving technologies and global connectivity.
It is interesting to note that concepts fundamental to today's Internet, like hypertext, were developed during these early days by computer scientists like Ted Nelson. The Internet's expansion beyond government and academia led to the rise of online service providers, the first websites, and search engines. Throughout time, advancements in telecommunications and protocols created what we now know as the modern Internet—a vast network of interconnected devices allowing for global information exchange and communication.