According to the Mundaka Upanishad, two kinds of knowledge must be known—the lower knowledge (aparā vidyā), which includes the Vedas and rituals, and the higher knowledge (parā vidyā), which leads to the realization of the imperishable Brahman.
This higher knowledge is not imparted to just any student. The teacher is instructed to pass it only to a qualified disciple—one who has developed mental tranquility (śānta), has gained control over the senses (dama), and is free from worldly distractions. Such a student is deemed spiritually mature and capable of understanding the formless, eternal truth of Brahman.
Therefore, Option (A) is correct: it reflects the spiritual readiness required to receive the higher knowledge, as emphasized in Vedantic teachings.
Explanation of Other Options:
(B) Obedience alone is not sufficient for spiritual understanding.
(C) Stability and discipline are necessary, but serenity and sense control are explicitly mentioned as prerequisites.
(D) Mastery of the Vedas is associated with lower knowledge and does not guarantee spiritual realization.