So here is my take:
36. BUT OF THAT DAY AND HOUR KNOWETH NO MAN, NO, NOT THE ANGELS OF HEAVEN, BUT MY FATHER ONLY.
I believe that this verse and "THAT DAY" signal a change in topic to the second coming (parousia) of Christ. Mt.7: 20-22 Mt.11:22 Jn.5:25,29 Jesus has already explained what would happen to His own generation. Now He contrasts that which would relate to His second coming (parousia) or presence on earth.
36. BUT OF THAT DAY AND
HOUR KNOWETH NO MAN,
NO, NOT THE ANGELS OF HEAVEN, BUT MY FATHER
ONLY.
37. BUT AS THE DAYS OF NOE
WERE, SO SHALL ALSO
THE COMING OF THE SON OF MAN BE.
38. FOR AS IN THE DAYS
THAT WERE BEFORE THE
FLOOD THEY WERE EATING AND DRINKING,
MARRYING
AND GIVING IN MARRIAGE, UNTIL THE DAY
NOE ENTERED INTO THE ARK,
39. AND KNEW NOT UNTIL THE
FLOOD CAME, AND
TOOK THEM ALL AWAY; SO SHALL ALSO THE COMING
OF
THE SON OF MAN BE.
40. THEN SHALL TWO BE IN
THE FIELD; THE ONE SHALL
BE TAKEN, AND THE OTHER LEFT.
41. TWO WOMEN SHALL BE
GRINDING AT THE MILL;
THE ONE SHALL BE TAKEN, AND THE OTHER
LEFT.
Elaboration - Lu. 17:20 -
42. WATCH THEREFORE: FOR
YE KNOW NOT WHAT
HOUR YOUR LORD DOTH COME.
43. BUT KNOW THIS, THAT IF
THE GOODMAN OF THE
HOUSE HAD KNOWN IN WHATWATCH THE THEIF
WOULD
COME, HE WOULD HAVE WATCHED, AND
WOULD NOT HAVE SUFFERED HIS HOUSE
TO BE
BROKEN UP.
44. THEREFORE BE YE ALSO READY: FOR IN SUCH AN HOUR AS YE THINK NOT THE SON OF MAN COMETH. Lu.12:42-48
Our beloved Leola writes
“The word parousia does not necessarily denote both "an arrival and a consequent presence"; it commonly denoted just the arrival, such as a terminus or an end-point of a time period (such as a state of affairs continuing UNTIL someone arrives). It is trivially easy to find clear examples of this in Greek literature. The parousia itself would then be a sudden change of the situation as opposed to being itself a duration. That is how it is used in the synoptic apocalypse. It is used interchangeably with erkhomai, and is an event that occurs suddenly or unexpectedly. The comparison of the parousia to the Flood of Noah emphasizes the suddenness of the event that will END an ongoing state of affairs. What was arriving to those on the earth was the Flood itself; it wasn't "invisibly present" beforehand. And even if it was, what happened during those years long before the Flood that made the Flood go from "not present" to "present"? Don't you see the problem? "Two men will be in the field; one will be taken and the other left. Two women will be grinding with a hand mill; one will be taken and the other left" (v. 40-41). That pertains to the parousia, in analogy with the Flood, and it highlights the suddenness of the event; people would be in the midst of their daily activities when it happens, just as those before the Flood were in the midst of eating, drinking, and so forth. The arrival denoted by the parousia isn't invisible either; " For as the lightning cometh out of the east, and shineth even unto the west; so shall also the coming of the Son of man be. " (v. 27). Sure there would be a presence after this, but it isn't one unremarked upon by the world at large. It was going to be absolutely obvious, with a spectacle in the sky and with a loud trumpet call from the heavens."
This event then is obviously a future visible and world changing event that all Christians will see and are looking forward to. Hope you are too.
Vander