Katha-2-1-2-parācaḥ kāmānanuyanti

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

The natural tendency to see external objects which are not atman is the cause of the obstacle, i.e., ignorance, to the realisation of the âtman. Being, opposed to it, the desire of enjoyments pertaining to this world and to the next, external to self and held up by ignorance, is another obstacle. The realisation of the âtman being impeded by ignorance and desire, men with little intelligence pursue only external objects of desire. By that cause, they get into the meshes of widespread, i.e., omnipresent death, i.e., the combination of ignorance, desire and karma. Meshes] that which binds, consisting in the possession and deprivation of the body, the senses, etc. The meaning is that they fall into a continuous stream of manifold misery, such as birth, death, old age, sickness, etc., This being so, the intelligent, knowing the certain immortality of concentration in the pratyagâtman (the immortality of the Dêvâs and the rest is uncertain; but this consisting in concentration in the pratyagâtman is certain, because it does not increase or suffer diminution by karma); i.e., knowing this constant and unshakable immortality, the knowers of Brahman do not covet any, among the ephemeral objects here, i.e., in samsâra full of misery, because these objects are opposed to the realisation of the pratyagâtman. The drift is that they rise above the desires of sons, wealth and worlds.

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