Crepuscular rays are visible when you're facing away from the sun (hence their name, they generally exist when the sun is low). God rays are a fuzzier concept,

Crepuscular rays are visible when you're facing away from the sun (hence their name, they generally exist when the sun is low). God rays are a fuzzier concept, but I've generally heard it when the rays appear to converge towards a light source (hence the divine term I guess). You could say both expressions do refer to the same rays, but with opposite perspectives.