Classic Poem

The way I read a letter's this:
'T is first I lock the door,
And push it with my fingers next,
For transport it be sure.

And then I go the furthest off
To counteract a knock;
Then draw my little letter forth
And softly pick its lock.

Then, glancing narrow at the wall,
And narrow at the floor,
For firm conviction of a mouse
Not exorcised before,

Peruse how infinite I am
To — no one that you know!
And sigh for lack of heaven, — but not
The heaven the creeds bestow.