How does writing reflect the audiences and purposes for which it was intended ?

An audience is the group of people the writer is addressing. 

There are 3 main purposes for writing: (examples in text messages)

1) To inform: "not coming over tonight. Sorry x"

2) To persuade: "Please come over tonight. I have ice cream"

3) To entertain: "If you come over tonight I'll do the handstand whilst walking down the stairs"