I have posted the parable of the watchful servants as well as early church
father's Irenaeus understanding. His understanding is important as he was
taught by Polycarp, a disciple of apostle John. He explains below that
there are 3 resurrections during the tribulation period. For those
interested in this; read Chapter 34 of Book 5 of Irenaeus's writings.
Especially note he states Blessed and holy is he who takes parts in the
first resurrection. If Apostle John notes the "first resurrection", there
must be others. I personally see a resurrection at the 7th seal, 7th
trump, and after the 7 bowls.
 

  Luke  35"Be dressed ready for service and keep your lamps burning,
36like men waiting for their master to return from a wedding banquet, so
that when he comes and knocks they can immediately open the door for
him. 37It will be good for those servants whose master finds them
watching when he comes. I tell you the truth, he will dress himself to
serve, will have them recline at the table and will come and wait on
them. 38It will be good for those servants whose master finds them
ready, even if he comes in the second or third watch of the night. 39But
understand this: If the owner of the house had known at what hour the
thief was coming, he would not have let his house be broken into. 40You
also must be ready, because the Son of Man will come at an hour when you
do not expect him."

From the writings of Irenaeus

This is what the Lord declared: "Happy are those servants whom the Lord
when He cometh shall find watching. Verily I say unto you, that He shall
gird Himself, and make them to sit down [to meat], and will come forth and
serve them. And if He shall come in the evening watch, and find them so,
blessed are they, because He shall make them sit down, and minister to
them; or if this be in the second, or it be in the third, blessed are
they."306 Again John also says the very same in the Apocalypse: "Blessed
and holy is he who has part in the first resurrection