In this poem the narrator notices a lady in church, with a louse that is roving, unnoticed by her, around in her bonnet. The poet chastises the louse for not realising how important his host is, and then reflects that, to a louse, we are all equal prey, and that we would be disabused of our pretensions if we were to see ourselves through each other's eyes.
An alternative interpretation is that the poet is musing to himself how horrified and humbled the pious woman would be if she were aware she was harboring a common parasite in her hair.
There is also a Scottish country dance called Frae Many A Blunder Free Us which references words from the last verse.
Ye ugly, creepin, blastit wonner,
Detested, shunn'd by saunt an' sinner,
How daur ye set your fit upon her-
Sae fine a lady?
Gae somewhere else and seek your dinner
On some poor body.
Swith! in some beggar's haffet squattle;
There ye may creep, and sprawl, and sprattle,
Wi' ither kindred, jumping cattle,
In shoals and nations;
Whaur horn nor bane ne'er daur unsettle
Your thick plantations.
Now haud you there, ye're out o' sight,
Below the fatt'rels, snug and tight;
Na, faith ye yet! ye'll no be right,
Till ye've got on it-
The verra tapmost, tow'rin height
O' Miss' bonnet.
My sooth! right bauld ye set your nose out,
As plump an' grey as ony groset:
O for some rank, mercurial rozet,
Or fell, red smeddum,
I'd gie you sic a hearty dose o't,
Wad dress your droddum.
I wad na been surpris'd to spy
You on an auld wife's flainen toy;
Or aiblins some bit dubbie boy,
But Miss' fine Lunardi! fye!
How daur ye do't?
O Jeany, dinna toss your head,
An' set your beauties a' abread!
Ye little ken what cursed speed
The blastie's makin:
Thae winks an' finger-ends, I dread,
Are notice takin.
O wad some Power the giftie gie us
To see oursels as ithers see us!
It wad frae mony a blunder free us,
An' foolish notion:
What airs in dress an' gait wad lea'e us,
An' ev'n devotion!