Dispensationalism is the belief that “God sometimes changes the way He asks man to show Faith.” From a debate on theologyonline:

In other words, a more simplistic question might be, “Has the ‘gospel’ (good news) ever changed?” I would say it has. For example, if a person came to me and said, “Jeremy, what must I do to be saved?” Would it be reasonable to turn to back to Genesis and say, “Well, Noah and his family were saved by building an ark. I guess you should build an ark in order to be saved.” We all agree that the previous instruction would be foolish. No one disagrees that the “gospel” for today is, “Believe that Jesus Christ died for our sins, was buried and was resurrected.” However, in the example of Noah, we have no record of Noah “believing” that Jesus Christ would die for Noah’s sins. We have no record of Noah “believing” that Jesus Christ would rise from the dead. We do have a record of Noah showing faith by doing a physical act (Genesis 6:13-22). Because Noah did the “faith work” of building the ark, he was saved physically and spiritually from the flood. I believe that this idea is foundational for our discussion. This simple example shows that God asks men at different times to show faith in different ways to be saved.

Dispensationalism is not defined by specific content of gospels, but merely by the fact that there have been different gospels (Good News) to different people at different times. Different people at the same time might have different gospels, and the same people at different times might have different gospels. Context is key (who, where, what, when and why). When individuals claim that all dispensationalists teach “salvation by faith alone” or that “God is going to re-establish the national kingdom of Israel” they are missing the real definition of dispensationalism.

I have met dispensationalists who believe Jesus taught a works faith salvation to spiritual salvation. I teach that Jesus was not proclaiming salvation to heaven, but salvation in the present life. I have met dispensationalists who taught that the apostles taught works-baptism-faith but not symbolic law. I teach that they apostles taught symbolic law to the Jews. I have met dispensationalists who claim that Paul and the apostles taught the same gospel, one without works. I teach that the apostles were still very much in favor of the symbolic law and this led to conflicts with Paul throughout his ministry.

To be a dispensationalist, one does not have to embrace a certain gospel. To be a dispensationalist, one just has to believe that God sometimes changes how he requires men to show faith.