किं कर्म किमकर्मेति कवयोऽप्यत्र मोहिताः। तत्ते कर्म प्रवक्ष्यामि यज्ज्ञात्वा मोक्ष्यसेऽशुभात् ॥

kiṁ karma kim akarmeti kavayo ’pyatra mohitāḥ tat te karma pravakṣhyāmi yaj jñātvā mokṣhyase ’śhubhāt

"What is action, what inaction"? Even the wise are herein perplexed. Therefore I will declare to thee the action by knowing which thou shalt be loosed from evil.

In plain words: Krishna says even wise people get confused about what counts as action and what counts as not acting. He promises to explain it, so that Arjuna can be free from wrongdoing.