I want to know the symbolism (Christian/Catholic/general)of the piece
of art "Keltisches Kreuz 13" (1999) by artist Stefan Kandels.

Presumably, you've seen these webpages.

"Keltisches Kreuz 13":
http://www.stump.info/christ/

Stefan Kandels:
http://lebenskunst.ag-pro-design.de/vit-kandels.html

Yes. I am looking for the artists' intention in using the symbols he
did in the work...eg. why the earth is at the center of the
cross?...what are the circles representing...color use?...title of
piece -is this the 13th of a series?, or just an arbitrary number
assigned to this work?...does 13 have any trinitarian value?...needles
to say, I can draw my own conclusions, make my own meaning...I am
simply interested to find out if there is anything known about the
artists own vision/meaning/message on this particular piece. Thanks!