Arjuna was also a pure devotee, but he never chanted neither did Krishna asked him to do so. So why do you stress so much on the same?
Chanting the name of Krishna means to constantly remember Him. Although it may appear that Arjuna was not chanting like we chant on the beads, he was calling Him in great eagerness by different names like ‘O Yadava, O Keshava, O Madhava’. This is certainly a sign of great advancement. He was put in such an awkward situation by the will of Krishna that he had no other choice but to call out in great desperation.
The dealings between Arjuna and Krishna were under Krishna’s internal energy, however we are affected by Krishna’s external energy. In the beginning we do not have taste for the Holy Name, therefore we are asked to chant in a prescribed way. Therefore we stress on chanting so that we come to higher level, wherein we are able to chant in great eagerness.
Bhagavad-Gita 18.66 says that we should abandon all varieties of religion and surrender to the Lord. We find that in the case of demigod worshippers they are attached to meat eating and other vices, even when they start chanting a round a day, the level of surrender is not really very high. What should we do?
The particular verse you have quoted is one of the final instructions of Lord Krishna to Arjuna and requires a high level of faith and surrender. Krishna also says that one must not disturb the faith of other people as they may lose whatever little faith they have in Vedic knowledge. Rather than asking new devotees to give up demigod worship, meat eating it is more expedient to ask them to add Krishna to their lives and let the process of devotional service cleanse their material desires.
The Supreme Personality of Godhead, Krishna, is worshipable as a father is worshipable for his son. He is the spiritual master because He originally gave the Vedic instructions to Brahma and presently He is also instructing Bhagavad-gita to Arjuna; therefore He is the original spiritual master, and any bona fide spiritual master at the present moment must be a descendant in the line of disciplic succession stemming from Krishna. Without being a representative of Krishna, one cannot become a teacher or spiritual master of transcendental subject matter
Krishna’s devotees relate to Krishna in various relationships; one might treat Krishna as a son, or one might treat Krishna as a husband, as a friend, or as a master. Krishna and Arjuna are related in friendship. As the father tolerates, or the husband or a master tolerates, so Krishna tolerates
Arjuna was not the supreme knower, and his decision to fight or not to fight was confined to his limited discretion. Lord Krishna instructed that the individual is not all in all. The Supreme Personality of Godhead, or He Himself, Krishna, as the localized Supersoul, sits in the heart directing the living being. After changing bodies, the living entity forgets his past deeds, but the Supersoul, as the knower of the past, present and future, remains the witness of all his activities. Therefore all the activities of living entities are directed by this Supersoul. The living entity gets what he deserves and is carried by the material body, which is created in the material energy under the direction of the Supersoul. As soon as a living entity is placed in a particular type of body, he has to work under the spell of that bodily situation. A person seated in a high-speed motorcar goes faster than one seated in a slower car, though the living entities, the drivers, may be the same. Similarly, by the order of the Supreme Soul, material nature fashions a particular type of body to a particular type of living entity so that he may work according to his past desires. The living entity is not independent. One should not think himself independent of the Supreme Personality of Godhead. The individual is always under the Lord’s control. Therefore one’s duty is to surrender, and that is the injunction of the next verse.
The Lord tells Arjuna that basically there is no possibility of understanding the Supreme Truth, the Absolute Truth, the Supreme Personality of Godhead, simply by speculating, for the Supreme Truth is so great that it is not possible to understand Him or to achieve Him simply by making a mental effort. Man can go on speculating for several millions of years, and if he is not devoted, if he is not a lover of the Supreme Truth, he will never understand Krishna, or the Supreme Truth. Only by devotional service is the Supreme Truth, Krishna, pleased, and by His inconceivable energy He can reveal Himself to the heart of the pure devotee. The pure devotee always has Krishna within his heart; and with the presence of Krishna, who is just like the sun, the darkness of ignorance is at once dissipated. This is the special mercy rendered to the pure devotee by Krishna
Arjuna is reluctant even to kill his enemies, let alone his relatives. He thinks that by killing his kinsmen there would be no happiness in his life, and therefore he is not willing to fight, just as a person who does not feel hunger is not inclined to cook. He has now decided to go into the forest and live a secluded life in frustration. But as a kshatriya, he requires a kingdom for his subsistence, because the kshatriyas cannot engage themselves in any other occupation. But Arjuna has no kingdom. Arjuna’s sole opportunity for gaining a kingdom lies in fighting with his cousins and brothers and reclaiming the kingdom inherited from his father, which he does not like to do. Therefore he considers himself fit to go to the forest to live a secluded life of frustration.
This Gitopanishad, Bhagavad-gita, the essence of all the Upanishads, is just like a cow, and Lord Krishna, who is famous as a cowherd boy, is milking this cow. Arjuna is just like a calf, and learned scholars and pure devotees are to drink the nectarean milk of Bhagavad-gita.
The Vedas, like the Mundaka Upanishad, as well as the Svetasvatara Upanishad, compare the soul and the Supersoul to two friendly birds sitting on the same tree. One of the birds (the individual atomic soul) is eating the fruit of the tree, and the other bird (Krishna) is simply watching His friend. Of these two birds — although they are the same in quality — one is captivated by the fruits of the material tree, while the other is simply witnessing the activities of His friend. Krishna is the witnessing bird, and Arjuna is the eating bird. Although they are friends, one is still the master and the other is the servant. Forgetfulness of this relationship by the atomic soul is the cause of one’s changing his position from one tree to another, or from one body to another. The jiva soul is struggling very hard on the tree of the material body, but as soon as he agrees to accept the other bird as the supreme spiritual master — as Arjuna agreed to do by voluntary surrender unto Krishna for instruction — the subordinate bird immediately becomes free from all lamentations.