Following is an extract from a Rabindranath Tagore story called, "A Wrong Man in Workers' Paradise". I need help in understanding the contextual meaning of a line in it.
The story is about a man who never did any useful work and lived a leisurely life devoid of all care.
Some boys seldom ply their books and yet pass their tests. A similar thing happened to this man. He spent his earth life in useless work and yet after his death, the gates of Heaven opened wide for him.
But, the Moving Finger writes even in Heaven. So, it came to pass that the aerial messenger who took charge of the man, made a mistake and found him a place in Workers' Paradise.
In this Paradise you find everything except leisure.
Upon a quick search over the Internet I found this explanation to the phrase.
However, I am not sure –
a) what 'Moving Finger' means here
b) what figure of speech is used
c) what is the contextual meaning of the whole phrase