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MM mantra 23

nāthe dhātari bhogi-bhoga-śayane nārāyaṇe mādhave
deve devaki-nandane sura-vare cakrāyudhe śārṅgiṇi
līlāśeṣa-jagat-prapañca-jaṭhare viśveśvare śrīdhare
govinde kuru citta-vṛttim acalām anyais tu kiṁ vartanaiḥ
Synonyms: 
nāthe — on your master; dhātari — and sustainer; bhogi — of the serpent (Ananta Śeṣa); bhoga — on the body; śayane — who lies down; nārāyaṇe mādhave — known as Nārāyaṇa and Mādhava; deve — the Supreme Lord; devaki-nandane — the darling son of Devakī; sura-vare — the hero of the demigods; cakra-āyudhe — the holder of the disc; śārṅ-giṇi — the possessor of the bow Śārṅga; līlā — as a pastime; aśeśa — endless; jagat — universes; prapañca — manifestation; jaṭhare — in the stomach; viśva — of the universes; īśvare — the controller; śrīdhare — the Lord of Śrī; govinde — on Lord Govinda; kuru — place; citta — of your mind; vṛttim — the workings; acalām — without deviation; anyaiḥ — other; tu — conversely; kim — what is the use; vartanaiḥ — with engagements.
Translation: 
Think only of your master and sustainer, the Supreme Lord, who is known as Nārāyaṇa and Mādhava and who lies on the body of the serpent Ananta. He is the darling son of Devakī, the hero of the demigods, and the Lord of the cows, and He holds a conchshell and the bow Śārṅga. He is the husband of the goddess of fortune and the controller of all the universes, which He manifests from His abdomen as a pastime. What will you gain by thinking of anything else?
Purport: 

In previous verses King Kulaśekhara has instructed his own mind to be fixed at the lotus feet of Kṛṣṇa, and now he instructs his readers to fix their minds on Him as well. He gives some of the Lord's innumerable names, which describe His qualities and pastimes. Devotees are attracted to serving a specific aspect of the Supreme Lord according to their specific rasa, or loving relationship with Him. One may meditate on and serve any bona fide form of the Lord and derive the same benefit of going back to Godhead. While passing away from the world, Grandfather Bhīṣma, who was in a chivalrous relationship with Kṛṣṇa, chanted prayers recalling that aspect of the Lord. Praying that his mind would go unto Kṛṣṇa, he reviewed the Lord's chivalrous pastimes in his mind: "May He, Lord Śrī Kṛṣṇa, the Personality of Godhead, who awards salvation, be my ultimate destination. On the battlefield He charged me, as if angry because of the wounds dealt by my sharp arrows. His shield was scattered, and His body was smeared with blood due to the wounds" (SB 1.9.38).

In this verse King Kulaśekhara instructs us to attain samādhi, or ecstatic concentration on the Supreme. Yogīs try to achieve samādhi by perfecting the eightfold yoga process, but this is very difficult. When Kṛṣṇa recommended this practice to Arjuna, he replied, "O Madhusūdana, the system of yoga You have summarized appears impractical and unbearable to me, for the mind is restless and unsteady.... [Controlling the mind] is more difficult than controlling the wind" (Bg. 6.33-34).

By contrast, bhakti-yoga is so easy that anyone can successfully practice it. A sincere soul who chants and hears the holy names of Kṛṣṇa, and also hears His pastimes and qualities narrated by self-realized devotees, can progress to the highest stages of concentration with an ease unknown to the followers of other yoga processes.

Why does King Kulaśekhara deem as worthless all activities except fixing the mind on Kṛṣṇa? Because all other acts and thoughts are temporary and thus lead to unending entanglement in material misery. As Śrīla Prabhupāda writes in his Bhagavad-gītā commentary, "If one is not in Kṛṣṇa consciousness, there cannot be a final goal for the mind." By the tricks of fate and the inexorable workings of karma, what appears auspicious and happy one moment may turn into tragedy the next. Like the Supreme Lord, the soul is sac-cid-ānanda-vigraha [Bs. 5.1] (eternal and full of bliss and knowledge), and as such he can be fully satisfied only when he unites in bhakti with the Lord. We should join with Bhīṣmadeva in praying, "May His lotus feet always remain the objects of my attraction."