vimukta-saṅgaṁ mana ādi-pūruṣe
kṛṣṇe lasat-pīta-paṭe catur-bhuje
puraḥ sthite ’mīlita-dṛg vyadhārayat
In the momentous hour of leaving his material body, Bhīṣmadeva set the glorious example concerning the important function of the human form of life. The subject matter which attracts the dying man becomes the beginning of his next life. Therefore, if one is absorbed in thoughts of the Supreme Lord Śrī Kṛṣṇa, he is sure to go back to Godhead without any doubt. This is confirmed in the Bhagavad-gītā (8.5-15):
5: And whoever, at the time of death, quits his body remembering Me alone at once attains My nature. Of this there is no doubt.
6: Whatever state of being one remembers when he quits his body, that state he will attain without fail.
7: Therefore, Arjuna, you should always think of Me in the form of Kṛṣṇa and at the same time carry out your prescribed duty of fighting. With your activities dedicated to Me and your mind and intelligence fixed on Me, you will attain Me without doubt.
8: He who meditates on the Supreme Personality of Godhead, his mind constantly engaged in remembering Me, undeviated from the path, he, O Pārtha [Arjuna], is sure to reach Me.
9: One should meditate upon the Supreme Person as the one who knows everything, as He who is the oldest, who is the controller, who is smaller than the smallest, who is the maintainer of everything, who is beyond all material conception, who is inconceivable, and who is always a person. He is luminous like the sun and, being transcendental, is beyond this material nature.
10: One who, at the time of death, fixes his life air between the eyebrows and in full devotion engages himself in remembering the Supreme Lord will certainly attain to the Supreme Personality of Godhead.
11: Persons learned in the Vedas, who utter oṁkāra and who are great sages in the renounced order, enter into Brahman. Desiring such perfection, one practices celibacy. I shall now explain to you this process by which one may attain salvation.
12: The yogic situation is that of detachment from all sensual engagements. Closing all the doors of the senses and fixing the mind on the heart and the life air at the top of the head, one establishes himself in yoga.
13: After being situated in this yoga practice and vibrating the sacred syllable oṁ, the supreme combination of letters, if one thinks of the Supreme Personality of Godhead and quits his body, he will certainly reach the spiritual planets.
14: For one who remembers Me without deviation, I am easy to obtain, O son of Pṛthā, because of his constant engagement in devotional service.
15: After attaining Me, the great souls, who are yogīs in devotion, never return to this temporary world, which is full of miseries, because they have attained the highest perfection.
Śrī Bhīṣmadeva attained the perfection of quitting his body at will and was fortunate enough to have Lord Kṛṣṇa, the object of his attention, personally present at the time of death. He therefore fixed his open eyes upon Him. He wanted to see Śrī Kṛṣṇa for a long time out of his spontaneous love for Him. Because he was a pure devotee, he had very little to do with the detailed performance of yogic principles. Simple bhakti-yoga is enough to bring about perfection. Therefore, the ardent desire of Bhīṣmadeva was to see the person of Lord Kṛṣṇa, the most lovable object, and by the grace of the Lord, Śrī Bhīṣmadeva had this opportunity at the last stage of his breathing.