What's the point of the 1000 yr reign?

[Arphaxad]

Firstly, I believe we will be priests of God and of Christ, and shall reign with him a thousand years(Rev. 20:6).
Who is it that we will reign over?
Will the ones we reign over be able to be saved?
Will the plan of salvation (Acts 2:38) still be in effect? or will it be some other way?
If people are not still being saved than what's the point? Just to reign over a bunch of lost souls?