But let us, since we belong to the day, be sober, putting on the breastplate of faith and love, and, for a helmet, the hope of salvation.

 Very naturally the New Testament writers to all intents and purposes identified the Day of the Lord with the day of the Second Coming of Jesus Christ. We will do well to remember that these are what we might call stock pictures. They are not meant to be taken literally. They are pictorial visions of what would happen when God broke into time. 