Alexander Pope (1688–1744) penned this line in or around 1711 when he was only 22 years old. It comes from one of his earliest pieces which he published anonymously and titled, An Essay on Criticism. Composed as a poetic essay in heroic couplets, it thematically centers on instructing contemporary critics and writers in graceful, proper ways of conducting literary criticism and literary art.

In the original context, “fools” refers to critics and well-read writers who come across in their publications and social interactions as self-absorbed know-it-alls. Pope warns against this behavior by likening such a person’s speech or writings to “rattling nonsense.” To Pope, a better mode of expression employs both sense and modesty, which he equates to angelic discernment. 

“The bookful blockhead ignorantly read,
With loads of learnèd lumber in his head,
With his own tongue still edifies his ears,
And always listening to himself appears. […]
No place so sacred from such fops is barred,
Nor is Paul's Church more safe than Paul's Churchyard:
Nay, fly to altars; there they'll talk you dead,
For fools rush in where angels fear to tread.
Distrustful sense with modest caution speaks,
It still looks home, and short excursions makes;
But rattling nonsense in full volleys breaks,
And, never shocked, and never turned aside,
Bursts out, resistless, with a thundering tide.”
(An Essay on Criticism, 612-630)

Pope wrote this essay in response to controversies within his contemporary literary world. Due to the growth of public literacy and vast accessibility of print in the 18th century, literary art was available to common men and women as well as to aristocrats. This enabled public conversations between all classes, which often involved highly satirical stories, poems, and essays designed to point out societal inconsistencies. In other words, Pope’s era was full of public and popularized literary criticism, which made it a timely and necessary subject of exploration.