In reference to dealing with sin in Millennium–I ‘m not sure there will be sin during the millennium, certainly Satan’s demonic spirits will be at work trying, but since Satan is bound during this time I believe the people living then are able to resist sinning. When Satan is released for a short while at the end I believe the ones he goes to gather are his demons who have been trying but failing to accomplish this. They are the number as the sands of the sea that gather to do final battle.
There are two big mistakes people make where Satan is concerned. One is to deny his existence, and the other is to blame him for everything. Certainly Satan is responsible for introducing sin into the world. But having inherited a sin nature as a result of helping him, man in his natural state is unable to refrain from sinning, even with Satan out of the picture. Evidence for this can be found in Ezekiel where sin offerings during the Millennium are mentioned 14 times in Ezekiel 40-46.