Katha-1-2-6-na sāmparāyaḥ

Sri Shankara’s Commentary (Bhashya) translated by S. Sitarama Sastri

Therefore alone, i.e., being ignorant, the way to the other world shines not for him. Sâmparâyah, the other world. Sâmparâyah, some means pointed out by the Sâstras and leading to the attainment of the other world; that means does not shine for the benefit of the ignorant man who is led astray, his mind being engrossed by such benefits, as son, cattle, etc., and who is enveloped by the darkness Of ignorance caused by wealth. Constantly thinking that this world alone which is perceived and which consists of women, food, drink, etc., exists, and that there is no other invisible world, he is born again and again and becomes subject to me, i.e., Death. The meaning is that he becomes subject to be tossed in grief, such as birth, death, etc., such is the world in general.

Links
Various resources on the Kathopanishad
Upanishad Series – Katopanishad Commentary by Swami Chinmayananda