Mark's Gospel begins with a title that raises questions: The beginning of the Gospel of Jesus Christ, the Son of God. That little word "of" substitutes for a complex concept in Greek grammar called the genitive case. This case has a wide variety of potential meanings when one tries to understand it from the perspective of a language like English; it is a highly flexible grammatical structure. It could mean that this is the beginning of the gospel about Jesus Christ. It could mean that is the beginning of the gospel (or "good news") that belongs to Jesus Christ, like in Mk 1:14, where Jesus announces the "gospel of God". This is the exact same relationship as the title, but here it seems more clearly to mean that this is God's gospel for God's people: "The time is fulfilled and God's kingdom (again same relationship, but here clearly a possessive) has drawn near (more on this later); repent and believe the gospel." The last major option for the title's genitive relationship is the gospel/good news that is Jesus Christ. Among these three, it is difficult to choose. After all, what comes in the following chapters could easily be the gospel that is about Jesus. It could also be the gospel that Jesus possesses as he turns quickly to announce a gospel. Finally, it is not hard for it to be argued that Jesus being the Messiah, being the Son of God - as will be revealed over the course of the Gospel of Mark - is itself the gospel.
It is important to remember that it is possible we are forcing a choice on to the ancient Greek in which this text was composed that is not necessary or even helpful when trying to understand the Greek. These ancient Jewish/early Christian texts are truly written in a foreign language and perhaps it is only the English-formed brains in us that makes us want to force the Greek constructs into the categories that make sense to us. Perhaps all of these shades of meaning (and more) could be held by the ancient person writing or reading this text.
