Mundaka-3-2-4-nāyamātmā

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

Com.—Combined with the wish to realise the Atman, strength, absence of excitement, and knowledge coupled with Sanyasa are helps; because this Atman cannot be attained by one devoid of strength produced by concentration on the Atman or by excitement caused by associating with objects of the world, as son, cattle and the rest, or by tapas devoid of linga. ‘Tapas’ here means ‘knowledge.’ “Linga,” means “Sanyasa.” The meaning is that the Atman cannot be attained by knowledge without Sanyasa. But of the knower who, with these aids, strength, absence of excitement, Sanyasa and knowledge—strives intent after the Atman, the Atman enters its abode, the Brahman.

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