What does 'Il Won Sang' mean?

In Won Buddhist temples, Buddha statues are replaced by the Il Won Sang image. The circular Won is not an object of worship but rather a symbol that points to the Dharmakaya Buddha, the truth that all Buddha, Bodhisattvas and sages enlighten to and the original nature of all sentient beings.

This Il Won Sang can literally be translated as, 'One circle image'.

 Il = one    Won = circle     Sang = image.

“Before the buddhas of antiquity appeared, there was a perfectly round shape.”

— Ancient Koan

Won literally means circle and symbolizes the ultimate reality. From ancient times many spiritual traditions have expressed the universal truth through the image of a circle. In early Christianity, God was depicted by a circle and in the Zen tradition, Buddha nature or our original mind has been symbolized by a circular image.
In Won Buddhist temples, the Buddha image is replaced by the Il Won Sang image. The western philosopher Descartes said, "I think, therefore I am." One Zen master asked, "If you do not think, who are you?" There is a koan or spiritual question in Zen that states, "Before the buddhas of antiquity appeared, there was a perfectly round shape." 
When our minds are without any defilements, desires, or attachments, we are as clear as space and as clean and purely reflective as a perfect mirror. This is the realm before any thought arises. This is beginner’s mind. This is who we really are.
In this pure space, all religions, all traditions, all philosophies can join together. This is our true home to which we all may return.