It can also be construed as the soul and or lord.
The upper half, or as above would represent the invisible spiritual world which is derived both ancient and modern conceptions of heaven and the empyrean. The most simple explanation would be that it is an ancient Gnostic symbol representing both the upper and lower halves of our world. The seen and unseen. You will find many adaptations of this cross such as the Celtic cross, The cross within a circle is an ancient symbol that you will find used by many ancient cultures and religions even to this very day.
