What is the millenium for?

The millenium is a 1000 year period that starts the day Christ returns.

The moment Christ returns, we that are alive (still in the flesh), will instantly return to our spiritual bodies. The flesh will literally melt off (I Corinthians 15:51-52). And, all those that passed away prior to Christ's return will also be there in their spiritual bodies.

The purpose of the millenium is for teaching God's Word to those that were not saved, so all people that ever lived will have a chance to be saved and live forever with Christ, but they must accept Him in order to change from a mortal body to an immortal body (1 Corinthians 15:53-57). All souls will be changed to their spiritual body, those still alive when Christ returns and those that died before His return. We will all be alive in our spiritual bodies for 1000 years when He returns.

This is also the time when satan will be cast into the bottomless pit and held there for the duration of the millenium (Revelation 20:1-3) and will have no influence during this time of great teaching. This means that people will not have any of the hang ups of the flesh (sickness, disease, etc.) and they will not have satan trying to deceive them in any way. It wil be a great time of teaching by Christ and His elect (Revelation 20:6).

So, those that were not saved before Christ returned will still be liable to die (mortal) and must wait until the end of the millenium to know if they will be saved. During the millenuim will be their chance to be saved so that they will have an immortal body when it ends with judgement day. Those that were saved prior to Christ's return will already have an immortal body and will have no concern about the second death and some will reign and teach with Christ, and even be able to help family members that were not saved (Revelation 20:6).

After the 1000 years expires, satan will be let out of the bottomless pit for a short time in order to test those that did not make the first resurection (not saved), to see if they will stand against satan and become saved or if they will follow him (Revelation 20:7-8). Unfortunately, many of the unsaved will be deceived by satan, again, and will come up to fight against those that did not follow satan this time to try and defeat them. But satan and his new followers will lose quickly and decisevely and will be destroyed for good (Revelation 20:9-10).