Do not yield to cowardice, Partha. It does not suit you. Cast aside this petty feebleness of heart and stand up, O scorcher of foes. Every word here is chosen to sting — not out of cruelty, but out of urgency. Krishna is speaking the way a father might speak to a son who has frozen at the edge of a swimming pool: You can do this. This hesitation is beneath you.
Krishna uses two names for Arjuna in the same breath. Partha — son of Kunti — reminds him of his mother's strength and lineage. Parantapa — scorcher of enemies — reminds him of his own proven power on the battlefield. The names themselves are the argument. You are not the person this behaviour belongs to.
The command 'uttishtha' — stand up — is among the most direct words in the Gita. No philosophy yet, no metaphysics. Just: get up. The teaching will come, but first, the student must be willing to rise.