Sirius is sending Harry a message, spiritual of coarse considering he's dead, he's like Harry's guardian angel.
Fear
Fear is something from within
Something that seems to hide
It comes when you are weak
And destroys your barriers from inside
And once it is released
There is no way to control
The powerful flow of emotions
And damage starts to take its toll
It won't stop either
Not unless you give in
Or if you fight until the end
But still you might not win
Only you can over come this evil
As you are its creator
And you can also be its destroyer
If you can hold out a little more
So take my word for this
No matter is going to happen
Just remember
To never give in