That is, it is used as a letter in an opening verse of a chapter in the Quran. The Quran is a form of communication. The Quran is Allah's communication to the creation. The same Quran is our means of communicating with Allah.
All communication is either by spoken word or written word.
Even the sign language for deaf people is written word. We either communicate by tongue or by hand. There is a third form of communication which is by thought. In this day and age, there is great emphasis on communication. However, the first form of communication most of us learn in childhood is the communication by tongue.