For whom was Mark writing? It is easier to make sense of the text if we read it in light of what the author intended, and that in turn would be heavily influenced by the audience he wrote for. Mark likely wrote for one specific Christian community, the one he was part of. He certainly cant be read as if he were addressing all of Christendom down through the ages, centuries after his own life ended.
The importance of Marks audience cannot be underestimated because it plays an important literary role. The audience is a privileged observer which experiences things otherwise only available to certain characters like Jesus. Right at the beginning, for example, when Jesus is baptized there is a voice from heaven saying Thou art my beloved Son, in whom I am well pleased. Only Jesus seems to be aware of this Jesus and the audience, that is. If Mark wrote with a particular audience and particular expected reactions in mind, we have to understand the audience in order to better understand the text.
There is no real consensus on identity of the audience Mark was writing for. The traditional position has been that the balance of evidence indicates that Mark was writing for an audience that, at the very least, consisted largely of non-Jews. This argument rests upon two basic points: the use of Greek and the explanation of Jewish customs.
First, Mark was written in Greek rather than Aramaic. Greek was the lingua franca of the Mediterranean world of that time, while Aramaic was the language common to the Jews. Had Mark been interested in addressing Jews specifically, he would have used Aramaic. Furthermore, Mark interprets Aramaic phrases for the readers (5:41, 7:34, 14:36, 15:34), something that would have been unnecessary for a Jewish audience in Palestine.
Second, Mark explains Jewish customs (7:3-4). Jews in Palestine, the heart of ancient Judaism, certainly didnt need Jewish customs explained to them, so at the very least Mark must have expected a sizable non-Jewish audience reading his work. On the other hand, Jewish communities well outside Palestine may not have been familiar enough with all the customs in order to get by without at least some explanations.
For a long time it was thought that Mark was writing for an audience in Rome. This is partly because of the association of the author with Peter, who was martyred in Rome, and partly on the assumption that the author wrote in response to some tragedy, like perhaps the persecution of Christians under emperor Nero. The existence of many Latinisms also suggests a more Roman environment for the gospels creation.
All over the Roman empire, the late 60s and early 70s were an ominous time for Christians. According to most sources, both Peter and Paul were killed in the persecution of Christians in Rome between 64 and 68. James, leader of the church in Jerusalem, had already been killed in 62. The Roman armies invaded Palestine and put large numbers of Jews and Christians to the sword.
Many sincerely felt that the end times were close. Indeed, all of this may have been the reason for the author of Mark to collect the various stories and write his gospel explaining to Christians why they had to suffer and calling others to heed Jesus' call.
Today, however, many believe that Mark was part of a community of Jews and some non-Jews in either Galilee or Syria. Marks understanding of Galilean geography is fair, but his understanding of Palestinian geography is poor he wasnt from there and couldnt have spent much time there. Marks audience probably consisted of at least some Gentile converts to Christianity, but the bulk of them were more likely Jewish Christians who didnt need to be educated in depth about Judaism.
This would explain why he was able to make many assumptions about their knowledge of Jewish scriptures but not necessarily their knowledge of Jewish customs in Jerusalem or Aramaic. At the same time, though, when Mark does quote from Jewish scriptures he does so in Greek translation evidently his audience didnt know much Hebrew.
Whoever they were, it seems likely that they were Christians suffering hardship because of their Christianity a consistent theme throughout Mark is a call to readers to identify their own sufferings with that of Jesus and thereby gain better insight into why they suffered. Its also likely that Marks audience was on the lower socio-economic levels of the empire. Marks language is more everyday than literary Greek and he consistently has Jesus attacking the rich while praising the poor.