The title of Hammett's novel The Maltese Falcon seems straightforward enough. The plot is centered on the search for the priceless statuette from Egypt, passed down through the centuries from kings to princes until it falls into the hands of Sam Spade.
But did you notice that the title is based on an object that only appears physically in two scenes out of the entire novel? Sure, it's talked about constantly by nearly all the characters, but its actual material presence is limited to the span of 5 pages out of 200. So in a way, the most important object of the whole novel is also the object that has the least stage time.
The Maltese falcon is known as a MacGuffin, a plot device in the form of some goal or desired object that the characters are willing to do and sacrifice almost anything to achieve or possess.
Usually, the exact details of the MacGuffin's importance are unexplained or sometimes not even integral to the narrative. All we need to know is that there's something all the characters want. Why they want it or why it's valuable is less important that the chase itself. In many ways, the Maltese falcon is the perfect example of a MacGuffin. It drives the plot forward, brings all the characters together (both good and bad), pits them against each other, but in the end, turns out to be completely worthless.
The Maltese Falcon can also be understood thematically in terms of corruption and greed. The fact that everyone is trying to get their hands on this priceless gem, at whatever cost, suggests that human greed is a destructive force that will stop at nothing.
Think of a wrecking ball demolishing an old building. You wouldn't want to get in the way of that huge hunk of swinging metal, right? Same goes for all the characters searching for the falcon. They are ready to bulldoze anything or anyone standing in their way. Hammett is trying to send a message about the relentless pursuit of wealth.