Abstergo, consisting of pretty much the modern Templars, a secret organization that claims that they are responsible for most of the world's new inventions, and are working on a new project that involves you. Why? To discover a lost treasure, a Piece of Eden. They use this machine, the Animus, to access your memories and your ancestor's memories to reveal the location of it. They do this by finding it in your DNA, as DNA contains memories from past generations, which is the same way animals know where to go in the certain times of the year.
The Third Piece of Eden is what Abstergo claims to be an ancient artifact with the power of mind control. They believe it is the cause of religion since it can cause illusions, like the parting of the red sea. They plan to send it into space and use some kind of machine to make it use it's power to take over the minds of everyone in the world. They think it will be an alternative for the corrupt world we live in since they would then be able to control the violence, economy, etc. through the control they will have over everyone's mind.