You are all children of light, and children of the day. We don't belong to the night, nor to darkness,
we are not of the night, nor of darkness: These expressions are in contrast to what has just been said. It may have been Paul’s intention to remind his readers they will finally bask in the glory of the day of the Lord while those whose deeds have been of the night (5:7) will be plunged into eternal darkness (Matthew 25:30). It should also be noted that "of darkness points to nature and origin. To belong to darkness is more than to be in darkness" (Vincent, Vol. IV 45).