Katha-1-3-2-yaḥ seturījānānāmakṣaraṃ

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

The Nachikêta fire, which is, as it were, a bridge for persons performing sacrifices for the purpose of crossing grief, we can light up. Moreover, what is fearless, and what is the main support of the knowers of Brahman, who wish to go to the other shore of Samsâra, the immortal Brahman known as âtman, we can know. The meaning of the text is that both the unmanifested and the manifested Brahman, the goal of the knowers of Brahman, and those who perform Karma are worthy to be known.

It is a description of these that has been given in the previous text.

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