Here's how I understand it. I do believe it is a reference to His Second Coming (per context), but the thing is, it is
comparing Noah's day with that coming future day (2nd Coming), by saying
"AS"...
"As" what? Well, we must look at the following verse, too (Matthew 24:39), which says, "And
[they] knew not until the flood came, and took them all away. So shall also the coming of the Son of Man be." This is
the main point of these three verses... the point being, that even though Noah had preached of a coming flood for many years, the majority of people "
knew not until the flood came"... how can this possibly be?! Of course they had to "know"! Noah TOLD them what to expect!
Yet, they disregarded God's Word (via Noah) and
went about "living life" as if it would never end,
as if everything were the same as it had always been, completely denying the fact that
judgment was on its way, just as Noah had said.
"They knew not until"...
and this is how it will also be leading up to His Second Coming.
Many will continue on in their "unbelief" that the Judge is Coming. Even with all the "evidence" He will give during the trib...
I think it is showcasing "the attitude/mindset" of those in Noah's day (
THEY were eating and drinking, marrying and giving in marriage... and so they didn't acknowledge God's Word... but the future TRIB FOLKS won't necessarily be DOING those same exact things, literally
[it doesn't say THEY will]...
they WILL be exhibiting the same attitude AS in Noah's day [who
were literally "eating and drinking (etc), and knew not until..."], and therefore will also...
"know not until". Their attitude generally being that of "disregarding God's Word.")
Hope that made some sense.
(Sorry Castle...

)