I'm not an artist, at all. In this case I sourced a 3D model, in stl format, https://www.cgtrader.com/3d-print-models/art/sculptures/jesus-medallion-2
There are all kinds of stl files floating round, ebay sellers with 100s of decorative shapes.
The rest was done in CAM software, the basic shape is cut out with a regular end mill, then the rest was cut with a 3mm ball end mill.
Good example https://www.youtube.com/watch?v=2B8IauHd8Gg
I built a 3D printer a while ago, it gave me a good head start with cad/cam.