Why is Krishna asking Arjuna to give up the weakness of the heart?

In the third verse of chapter 2 of Bhagavad Gita for happiness, Krishna tells Arjuna that he does not pay heed to this ignorance. It is time to get rid of these petty weaknesses and fight the war. Krishna addresses Arjuna as Pitaputra as he is a blood relation — Kunti was Vasudev's sister. Krishna doesn't want Arjuna to give up his proper warrior form or Kshatriya dharma.