keep calm and read jane austen what does it mean?

There's a historical pedigree here.

In May-June 1939, the British and French Allied Forces made a great retreat at Dunkirk and fled back to Britain in disarray after a surprise German panzer assault. At the time, Britain expected Germany to quickly organize a cross-sea landing, so a set of three morale-boosting posters was printed in response to the possibility of a German occupation of the British mainland:

British posters

keep calm and read jane austen is an homage to the first " keep calm and carry on" poster.

The other two were "Freedom Is In Peril, Defend It With All Your Might" (***400,000 printed) and "Your Courage, Your Cheerfulness". Courage, Your Cheerfulness, Your Resolution Will Bring Us Victory" (***800,000 printed).

With Germany losing the air war against Britain, the Sea Lion plan to land in Britain was abandoned. The posters, which were printed in advance in the UK, were not used, and most of them were destroyed in secret. It wasn't until 2000 that the keep calm and carry on poster was found in a bookstore and quickly circulated. In the process of circulation, the words "keep calm and" were retained, but the content of the latter was spoofed in various ways, read jane austen being just one of them.