तस्मात्त्वमुत्तिष्ठ यशो लभस्व जित्वा शत्रून् भुङ्क्ष्व राज्यं समृद्धम्। मयैवैते निहताः पूर्वमेव निमित्तमात्रं भव सव्यसाचिन् ॥

tasmāt tvam uttiṣhṭha yaśho labhasva jitvā śhatrūn bhuṅkṣhva rājyaṁ samṛiddham mayaivaite nihatāḥ pūrvam eva nimitta-mātraṁ bhava savya-sāchin

Therefore stand up! win for thyself renown, Conquer thy foes, enjoy the wealth filled realm, By Me they are already overcome, Be thou the outward cause, left-handed one.

In plain words: Krishna tells Arjuna to get up and fight. He says the enemies are already defeated by him, and Arjuna only needs to be the one who carries it out. 'Left-handed one' is a name for Arjuna, who can shoot arrows with either hand.