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

> 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, and 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.

[Wikipedia]( says

> “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.

Near the beginning of the second stanza of “The Second Coming” we find:

> 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 merely 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’?