The word muni means one who can agitate his mind in various ways for mental speculation without coming to a factual conclusion. It is said that every muni has a different angle of vision, and unless a muni differs from other munis, he cannot be called a muni in the strict sense of the term. Nāsāv ṛṣir yasya mataṁ na bhinnam (Mahābhārata, Vana-parva 313.117). But a sthita-dhīr muni, as mentioned herein by the Lord, is different from an ordinary muni. The sthita-dhīr muni is always in Kṛṣṇa consciousness, for he has exhausted all his business of creative speculation. He is called praśānta-niḥśeṣa-mano-rathāntara (Stotra-ratna 43), or one who has surpassed the stage of mental speculations and has come to the conclusion that Lord Śrī Kṛṣṇa, or Vāsudeva, is everything (vāsudevaḥ sarvam iti sa mahātmā su-durlabhaḥ). He is called a muni fixed in mind. Such a fully Kṛṣṇa conscious person is not at all disturbed by the onslaughts of the threefold miseries, for he accepts all miseries as the mercy of the Lord, thinking himself only worthy of more trouble due to his past misdeeds; and he sees that his miseries, by the grace of the Lord, are minimized to the lowest.
(Bhagavad-Gita-----2:56-----purport).

Those who are worshipers of demigods have been described as less intelligent persons, and here the impersonalists are similarly described. Lord Kṛṣṇa in His personal form is here speaking before Arjuna, and still, due to ignorance, impersonalists argue that the Supreme Lord ultimately has no form. Yāmunācārya, a great devotee of the Lord in the disciplic succession of Rāmānujācārya, has written two very appropriate verses in this connection. He says,
tvāṁ śīla-rūpa-caritaiḥ parama-prakṛṣṭaiḥ
sattvena sāttvikatayā prabalaiś ca śāstraiḥ
prakhyāta-daiva-paramārtha-vidāṁ mataiś ca
naivāsura-prakṛtayaḥ prabhavanti boddhum
"My dear Lord, devotees like Vyāsadeva and Nārada know You to be the Personality of Godhead. By understanding different Vedic literatures, one can come to know Your characteristics, Your form and Your activities, and one can thus understand that You are the Supreme Personality of Godhead. But those who are in the modes of passion and ignorance, the demons, the nondevotees, cannot understand You. They are unable to understand You. However expert such nondevotees may be in discussing Vedānta and the Upaniṣads and other Vedic literatures, it is not possible for them to understand the Personality of Godhead." (Stotra-ratna 12)
(Bhagavad-Gita-----7:24-----purport).

Śrīla Yāmunācārya has recited this verse in his Stotra-ratna (43):
bhavantam evānucaran nirantaraḥ
praśānta-niḥśeṣa-manorathāntaraḥ
kadāham aikāntika-nitya-kiṅkaraḥ
praharṣayiṣyāmi sanātha-jīvitam
"By serving You constantly, one is freed from all material desires and is completely pacified. When shall I engage as Your permanent eternal servant and always feel joyful to have such a fitting master?"
Manorathenāsati dhāvato bahiḥ: (S.B.5:18:12) one who acts on the mental platform must descend to material activities. Material contamination, however, is completely absent from the Supreme Personality of Godhead and His pure devotee. Therefore the Lord is addressed as praśānta, completely peaceful, free from the disturbances of material existence.
(Srimad Bhagavatam-----9:8:24-----purport).

In Stotra-ratna (46), Yāmunācārya writes: "My Lord, those who keep themselves independent of Your service are helpless. They work on their own account, and they receive no support from superior authority. Therefore I long for the time when I shall engage fully in Your transcendental loving service without any desire for material satisfaction and without being confined to the mental plane. Only when I engage in such unalloyed devotional service will I enjoy actual spiritual life."
(Teachings of Lord Caitanya).

That Lord Kṛṣṇa is the original Supreme Personality of Godhead is accepted not only by Arjuna but by illustrious saints and sages like Vyāsadeva, Nārada, Devala, and Asita. All the previous spiritual preceptors, as well as present-day saints and countless millions of ordinary people, unanimously accept Lord Kṛṣṇa as the Supreme Godhead, but a famous paṇḍita like Dr. Radhakrishnan hesitates to accept Him as God! Why? Śrīla Yāmunācārya aptly explains in his Stotra-ratna:
tvāṁ śīla-rūpa-caritaiḥ parama-prakṛṣṭaiḥ
sattvena sāttvikatayā prabalaiś ca śāstraiḥ
prakhyāta-daiva-paramārtha-vidāṁ mataiś ca
naivāsura-prakṛtayaḥ prabhavanti boddhum
"O my Lord, those influenced by demoniac principles cannot realize You, although You are clearly the Supreme by dint of Your exalted activities, forms, character, and uncommon power, which are confirmed by all the revealed scriptures in the quality of goodness and the celebrated transcendentalists in the divine nature."
(Renunciation through Wisdom).