Dispensationalism
Crazy word.
Anyway, it's the study of dispensation, which basically means the various "stages" of God's presence in the world (and how He dealt with mankind) and the means by which humans were to worship.
First was the age of innocence--in the Garden of Eden. Adam and Eve were the first of this age and they were the ones who ended it by eating the forbidden fruit.
Next came conscience. Humans were guided by their consciences; their way of obeying and worshiping God was through doing what was right in their minds. Well, that didn't last, either. Flood.
After conscience was human government. Men were to rule the Earth and set up governments that would curb sin and praise God in this manner. Damn. Here come the plagues.
The promise--the Israelites were to inherit the promised land after they were freed by direct obedience to God. ...Oops.
Moses now was given the burden of the Law. Those who served God were to follow written codes and commands that God gave them. Didn't work.
In the current age, we are under the dispensation of grace--that we are saved through Christ alone, and that we are not bound by laws and regulations in our service to God. All we have to do is ask forgiveness and we are given it.
After this age, there will be the end times. The millennial kingdom, ruled by Christ. And after that...not much.