As far as I can tell, the function of this ritual is threefold:
1) To heighten the impression of total and permanent crisis, reinforcing the need for indefinite lockdowns;
2) To evoke traditional celebrations of military personnel and first responders, creating the impression that the viral outbreak is similar to a war or terrorist attack;
3) To generate a (fake) sense of community with strangers who are similarly confined to their homes (this being the only large-scale social activity still permitted), and therefore conditioning New Yorkers to accept, embrace and even enjoy their isolation and confinement as the “new normal.”
In summary, the purpose of these orchestrated clapping sessions – like the terrifying stories being spewed by the media and social media – is to manufacture consent for ongoing, massive political and societal changes that would otherwise be unacceptable.
*(The category of “essential workers” is quite broad; based on the city’s definition of “essential businesses or entities,” it seems to include bankers and journalists as well as healthcare workers treating WuFlu patients. By some accounts, the clapping is primarily directed at medical personnel, but other reports mention truck drivers, grocery store workers, etc. The vagueness of what categories of workers are being celebrated is another creepy aspect of the ritual. At least in Airstrip One, the clapping is specifically for the NHS.)