Even if someone is on the opposing side, it doesn't change the fact that they are a person who deserves respect.

Arjuna, who was told to "stand up," appeals to Bhishma and Drona as to why he cannot aim arrows at them. Although they are in the enemy army, they are elders and teachers whom he deeply respects. He feels that even a slight act of disrespect is a sin, and therefore he believes it is impossible for him to shoot sharp arrows at such people.

Arjuna calls Krishna by the name of "the one who destroyed demons like Madhu and enemies." He asks, "You, who have destroyed evil, why do you tell me to kill those worthy of respect?" This expresses his surprise. His problem is not simply a lack of courage in battle, but rather that he doesn't know how to deal with the unwavering respect and human relationships even when factions are divided.

Japanese Translation from the Geeta Press Edition - Chapter 2, Section 4: "Why am I being targeted with arrows by Bheeshma and Drona?"

As a response to the master's words, Arjuna presents two arguments in separate paragraphs, demonstrating the inappropriateness of fighting against elders who are objects of respect for him.

He then reiterates that he had considered his decision on this matter to be one with which he was completely resolved.

Sanskrit original text

अर्जुन उवाच
कथं भीष्ममहं सङ्ख्ये द्रोणं च मधुसूदन ।
इषुभिः प्रतियोत्स्यामि पूजार्हावरिसूदन ॥ ४ ॥

Romanization

arjuna uvāca
kathaṃ bhīṣmam ahaṃ saṅkhye droṇaṃ ca madhusūdana |
iṣubhiḥ pratiyotsyāmi pūjārhāv arisūdana || 4 ||

The meaning and translation of section 4 will continue on the next page.

Arjuna said, "Krishna, how can I possibly aim my arrows at Bhishma and Drona on the battlefield? They are individuals who deserve the deepest respect; they are those who destroy enemies." (4)

Arjuna expresses his surprise by calling the main character "the one who destroyed Madhu" or "the one who destroys enemies," and further using the word katham, which means "how."

The intention was to show that Bheeshma and Drona, who are encouraging the main character to fight, are not demons or enemies. Rather, they were highly respected elders.

In such a situation, why does the Lord advise Arjuna to fight against the elders, which goes against his own nature? Why can Arjuna involve himself in that terrible sin?

Arjuna uses the word Iṣubhiḥ, which means "by an arrow."

This indicates that, even directing light words towards elders who consider any utterance a great sin, it is impossible to challenge them with sharp arrows in battle.

Therefore, Arjuna was surprised as to why Bhagavan Shri Krishna would advise him to do something that appeared completely like a sinful act.