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MM mantra 40

satyaṁ bravīmi manujāḥ svayam ūrdhva-bāhur
yo yo mukunda narasiṁha janārdaneti
jīvo japaty anu-dinaṁ maraṇe raṇe vā
pāṣāṇa-kāṣṭha-sadṛśāya dadāty abhīṣṭam
Synonyms: 
satyam — the truth; bravīmi — I am speaking; manujāḥ — O humans; svayam — myself; ūrdhva — with raised; bāhuḥ — arms; yaḥ yaḥ — whoever; mukunda narasiṁha janārdana — O Mukunda, Narasiṁha, Janārdana; iti — thus saying; jīvaḥ — a living being; japati — chants; anu-dinam — every day; maraṇe — at the time of death; raṇe — during battle; — or; pāṣāṇa — stone; kāṣṭha — or wood; sadṛśāya — to a state of similarity with; dadāti — he renders; abhīṣṭam — his cherished desires.
Translation: 
O mankind, with arms raised high I declare the truth! Any mortal who chants the names Mukunda, Nṛsiṁha, and Janārdana day after day, even in battle or when facing death, will come to regard his most cherished ambitions as no more valuable than a stone or a block of wood.
Purport: 

Even those who sincerely endeavor for self-improvement know that it is very hard to quell cherished ambitions. Sometimes these ambitions are so grandiose that we keep them secret, yet we cherish them within. An obscure, untalented man thinks he may one day become the dictator of the world. An unpublished poet dreams he will become the next Shakespeare. And so on. The materialists are always being encouraged to fan the fires of their ambition; even children are encouraged by their parents to "get ahead."

But pure devotees of the Lord are well aware that all worldly ambitions are useless. Śrīla Bhaktisiddhānta Sarasvatī Ṭhākura, to instruct us, criticizes his own mind and asks, "Why are you after fame? Don't you know it is as worthless as the dung of a boar?" Śrīla Raghunātha dāsa Gosvāmī uses an equally graphic metaphor to criticize his mind in his Manaḥ-śikṣā, comparing the desire for fame to a filthy dog-eater dancing in his heart. Devotees, then, must always be vigilant that the subtle desire for name, fame, and high position, technically called pratiṣṭhāśā, does not arise within the heart, since it blocks pure love for Kṛṣṇa from entering there.

In contrast to a devotee, an impersonalist finds it impossible to cleanse his heart completely of materialistic ambition. Even after he subdues some of the grosser ambitions, he still maintains the impossible wish to "become God." Śrīla Prabhupāda called this desire to become one in all respects with the Absolute Truth "the last snare of Māyā." And the demigods, in their prayers to Kṛṣṇa while He was still in the womb of Devakī, have given the last word on the impersonalists' so-called liberation of merging with the Absolute Truth:

ye 'nye 'ravindākṣa vimukta-māninas
tvayy asta-bhāvād aviśuddha-buddhayaḥ
āruhya kṛcchreṇa paraṁ padaṁ tataḥ
patanty adho 'nādṛta-yuṣmad-aṅghrayaḥ

"O lotus-eyed Lord, although nondevotees who accept severe austerities and penances to achieve the highest position may think themselves liberated, their intelligence is impure. They fall down from their position of imagined superiority because they have no regard for Your lotus feet" (SB 10.2.32).

King Kulaśekhara advises us how to rid ourselves of all material ambitions: We should chant the holy names of God—Mukunda, Nṛsiṁha, and Janārdana. These are all names of Kṛṣṇa, and as such they are contained within the mahā-mantra: Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare. Chanting the names of Kṛṣṇa awakens one's love for Him, and then all one's material ambitions vanish. Śrīla Prabhupāda used to say that just as when someone gets a million dollars all his ten-dollar and hundred-dollar problems are automatically solved, so when we attain pure love for Kṛṣṇa all our petty material needs and desires pale to insignificance. Chanting the name of the Lord in pure ecstatic love puts the devotee in direct touch with the wonderful forms, qualities, and pastimes of the Lord; in that state the devotee is fully satisfied and loses all traces of egoistic ambition. He becomes happy simply to worship, serve, and be with the Supreme Personality of Godhead.

The history of Dhruva Mahārāja illustrates the purifying power of Kṛṣṇa consciousness. Dhruva sought out the Supreme Lord as a way to obtain a material kingdom. But after he had performed severe austerities and came face to face with Lord Viṣṇu, he declared, svāmin kṛtārtho 'smi varaṁ na yāce: [Cc. Madhya 22.42] "My dear Lord, I am fully satisfied. I do not ask from You any benediction for material sense gratification" (Hari-bhakti-sudhodaya).

Love of God is dormant within everyone, and to realize that love is to fulfill the purest ambition. The Vaiṣṇava ācāryas never advise us to try to kill our ambitious spirit; rather, they instruct us to desire only to awaken our taste for pure devotional service.