How do you initialize the value?
Also, you don't have to use + and str() to display text; just use &, which concatenates strings; it will automatically convert numbers to text that way. So,
"Character's HP is " & Characters(3,0)
Okay, I just realized it. The Array is 1-indexed; the 0 is out of bounds, it doesn't exist. Rows and columns begin at 1; you should be setting it to (3,1), not (3,0). Actually, you can skip the second number and it will automatically get the first row.