This verse seems to be out of place. It has caused much confusion and remains one of those mysteries of Revelation. With its placement right before the final judgment (next verse), the verse implies that there will be some persons who did NOT take the mark of the beast (Revelation 13:16), and, thus, should be "rescued" before the final battle. How this will happen is not stated; it probably is different than the up-taking we believers will experience if we live that long (1 Thessalonians 4:13-18).
(Behold, I AM COMING like a THIEF.
Before the tribulation, the believers at the church of the Thessalonians were informed of another thief-like event (1 Thessalonians 5:1-11). It, too, was given a 'day of the Lord' connotation (see previous verse).
Blessed is the one who stays AWAKE and keeps his garments,
While this could literally mean stay physically awake due to the time compress and the pending confrontation (next verse) which is being televised most certainly around the world, it also could mean staying awake spiritually. For one's garment to be taken away, one must be in a deep sleep. This may be a reference to those who prior to the tribulation KNEW the way to salvation but never made the commitment. Now they appear to be in a deep spiritual sleep.
lest he walk about NAKED and men see his SHAME.)
Nakedness is exposure; what may have been hidden is revealed. Shame shows pollution or being spotted with the worldly sin curse (1 John 2:26-29).
Recall that prior to Christ's crucifixion, he was exposed in a similar manner. At that time, his exposure was to all the sins of the world. That is why it is so gratifying to know that He now is fully clothed (Revelation 1:13). Tribulation saints, too, are dressed in like manner (Revelation 7:9).
ARE YOU WEARING GARMENTS (of righteousness) OR ARE YOU NAKED?