First the reason we are in the state that we are is because Eve was decieved, and Adam rebelled againsed God. (by the way, that senario is a type of christ, Adam a [a type of christ] gives him self for Eve [a type of the church] dies and then reunites with Eve outside of Eden). After that man could no longer speak to God directly because man because we were tainted by sin.
Then God continued to try to deal with man in new ways, first he tried dealing with man by dealing with his concience, at first it worked well, but it ultimitly ended in the total apostasy and ended in the flood.
Then after the flood to the Tower of Bable, God delt with man through human government, and again, at first man did well, but again it ended in total apostasy and God had to divid man at the Tower of Bable, then we have God using the Patriarcs, from Abraham, to Joesoph, but again ends in apostacy when the children of Israiel become slaves. Then God decides to deal with man by the Law, from Moses at the Mount of Zion, and lasted untill total apostacy at the Cross at Calvary. When Jesus gave his life on the cross, and rose from the dead, and then after the asention, God began to deal with man by grace. As you see every dispensation since the gargen of Eden, first begane perfect, but ends in total apostacy. The same will be for the age of Grace, at the rapture.
That is Pre Millenialism in a nut shell.
I hope that helps.