13.34 Yatha, as; ekam, the one; ravih, sun; prakasayati, illumines; imam, this; krtsnam, whole; lokam, world tatha, similarly;-who?-ksetri, the Knower of the field, i.e. the supreme Self, though one; prakasayati, illumines; krtsnam, the whole; ksetram, field, from the 'great elements' to 'fortitude' (cf. 5-6).
Here the illustration of the sun serves to highlight two aspects of the Self, viz that, like the sun, the Self is one in all the fields, and that It remains unaffected.
This verse is meant for summarizing the idea of the whole of this chapter: