Null Reference Exception when reading from array of strings

Hello, I am a little confused trying to make a simple (as I thought) thing. I delared a:

 public string[,] content;

then filled it with strings in a TextReader method:

 public void TextReader()
     {
         string[,] content = new string[2, 3];
         content [0, 0] = "A";
         content [0, 1] = "B";
         content [0, 2] = "C";
         content [1, 0] = "D";
         content [1, 1] = "E";
         content [1, 2] = "F";
         defaultText = "START";
         print (content [0, 0]);
     }

When I print content[0,0] from inside of the method everything is ok, but when I try to access content[0,0] or any other (content[1,2], content[0,2]) from outside I get a null exception error: object reference not set to an instance of an object.
I have put TextReader() in start:

 void Start () {
         TextReader ();
         print (content [0, 0]);
 }

And this gives me an error.

What I'm basically trying to do is put a text on a Text UI from the script. Maybe I'm missing something but if a variable is public should it be available from all methods? I'm new to programming so sorry if it's a simple misconception.