Purport

Bhagvan Shri Krishna explained the two paths of five lights. Those five lights are further classified into two groups. The three main experts, Shri Adi Shankara, Shri Ramanujacharya and Shri Madhvacharya put them into the group calling them 1. Path of splendor of sun and 2. The path of Splendor of Moon. Shri Adi Shankara further explained the two paths as 1. path of Knowledge 2. Path of fruitiness activities. One traveling through path free human from the cycle of birth and death. One who traverses on the second path has to return back to this mortal world. Shri Adi Shankara has explained this Shloka as follows:

Truly are the bright and dark paths,—the one is bright as there is illumination of Knowledge, and the other is dark because of the want of it,— of the world: they are open only to those (of the world) qualified for Knowledge or for action, and not for the entire world are the two paths possible (open);—considered regarded as, eternal, constant17, because samsāra is eternal. Of the two, by the one, the bright path, mangoes to return not; by the other (i.e. the dark path), he returns again.
---(Adi Shankaracharaya)