The purpose of Mark is established early. Mark doesn't waste time...or words. The key to understanding Mark is that it is a goalie of identity. The interactions around Jesus often focus on "who is this" who can do such a thing? Already in chapter one, after Jesus has cast out an unclean spirit, the people ask, "What is this? With what authority does he do this?" (1:27). This is the key theme throughout Mark.
But we can note a few things that go along with this. First, before Jesus cast out the unclean spirit, the spirit spoke, and called Jesus "the Holy One of God" (1:24). The demons knew who Jesus was. Second, the book is book-ended with the confession of the Roman (non-Jewish) centurion, "Truly this man was the Son for God!" (15:39). Third, in between these two confessions of faith, we find a myriad of reactions to Jesus. Some are positive, some are negative, but most are struggling to understand who Jesus is. We see this especially on the part of the disciples in chapters 8-10.
So the question Mark is asking is, Do you know who Jesus is? Because that question will change you.