There is the following statement in Jeffery Archer’s fiction “Kane & Abel,” in which William Kane, one of two heroes looks at his wife sleeping soundly on bed:

> “He put the phone down and looked across at the sleeping Kate,
> blissfully unaware of his latest problem, how he wished he could
> manage that. A curtain only had to flutter in the breeze and he would
> wake up. She would probably **sleep through the Second Coming.** He
> scribbled a few lines of explanation and put the note on her bed side
> table, then he dressed, packed, ad set off for New York.”

OALED defines ‘the Second Coming’ as a day in the future when Christians believe Jesus Christ will come back to earth.

The Wikipedia provides the definition: 

> “The Second Coming" is a poem composed by Irish poet William Butler
> Yeats in 1919 - -. The poem uses Christian imagery regarding the
> Apocalypse and second coming as allegory to describe the atmosphere in
> post-war Europe,”

accompanied with the poem including the word, the Second Coming:

> Surely some revelation is at hand;
> Surely the Second Coming is at hand.
> The Second Coming!  Hardly are those words out When a vast image out
> of Spiritus Mundi
> Troubles my sight:”

However, I’m not able to relate the above definitions of ‘the Second Coming’ to "mere" sleeping as used in the above lines of Archer’s.

Does “Sleep through the Second Coming” simply mean to sleep soundly, or have specific meaning? Why has it to be ‘the Second Coming’?