Arjuna refused to fight against the Kaurava army because his relative and his teacher were on the opposite side. If all that was needed was to convince Arjuna that he had to fight, Lord Krishna could have done so simply.
All that Arjuna needed to be convinced about was whether he should fight or not. Why did Krishna have to give a detailed discourse to him on the paths to moksha? The reason, to put it simply, was because of Arjuna’s use of the word ‘sreya.’ Arjuna was asking the Lord to tell him that which was good for Arjuna, that which would be right for him. What can be good for a person except to reach the Lord’s feet? And so it was that Krishna gave Arjuna the entire Bhagavad Gita, elaborated Valayapet Ramachariar, in a discourse.
What kind of a person was Arjuna? There are those who are completely ignorant of the difference between the body and the atma. Arjuna was not such a person. He was afraid of the sins of killing his Acharya and Bhishma. Sins attach not to the body, but to the atma. So he could see that there was a difference between body and atma. If he did not know the difference between body and soul, he would have had no ethical considerations at all, and would have fought without a thought. So clearly he did not belong to this category.
Did he have misplaced affection? Here again the answer is in the negative. After all, it cannot be termed wrong to have regard and affection for one’s Acharya and one’s grand-uncle.
Arjuna’s mistake was that he knew some things, but not everything that he needed to know, and what he knew he had not understood properly. It was right to have affection for Drona and Bhishma, but the context of the affection assumes importance.
Had Bhishma and Drona come as relative and Acharya, Arjuna’s affection could have been deemed apt. But they had come as enemies, ready to fight and kill. So his affection for them in this instance was not right.
Arjuna had to be made to realise that while he had to do his duty, the fruits were entirely in God’s hands. So for Arjuna’s good, the Lord had to give him a detailed discourse in the form of the Bhagavad Gita.