How does the cycle of rebirth work, and what is the ultimate key to becoming free from it?

Chapter 37 explains that the cycle of rebirth is perpetuated by the seeds of desires, much like a tree grows from a seed. If a person dies, another body is obtained through the 'seeds of action.' As long as desires persist, this cycle of rebirth continues with unhindered speed. The ultimate key to freedom is to destroy these desires at their very root. When desires are completely destroyed, the 'knot in the heart is removed,' which is described as the firm belief that 'Body is me.' Only then, as the Vedanta teaches, does a mortal man become immortal and escape the cycle.