In plain words
Perform the action that is yours to do, for action is better than inaction. Even the maintenance of your body would not be possible through inaction.
Word for word
Do you perform prescribed action, for action is better than inaction; and even the maintenance of your body would not be accomplished through inaction.
नियतं कुरु कर्म त्वं कर्म ज्यायो ह्यकर्मणःशरीरयात्राऽपि च ते न प्रसिद्ध्येदकर्मणः
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam
यतः एवम् अतः —
नियतं नित्यं शास्त्रोपदिष्टम् , यो यस्मिन् कर्मणि अधिकृतः फलाय च अश्रुतं तत् नियतं कर्म, तत् कुरु त्वं हे अर्जुन, यतः कर्म ज्यायः अधिकतरं फलतः, हि यस्मात् अकर्मणः अकरणात् अनारम्भात् । कथम् ? शरीरयात्रा शरीरस्थितिः अपि च ते तव न प्रसिध्येत् प्रसिद्धिं न गच्छेत् अकर्मणः अकरणात् । अतः दृष्टः कर्माकर्मणोर्विशेषो लोके ॥ ८ ॥
In plain words
Because it stands like this, therefore —
'Prescribed' simply means: constant, laid down by scripture. Whatever action someone is entitled to, so long as it isn't tied by scripture to any particular reward — that is prescribed action. That is what you should do, Arjuna. Because action, in terms of what it actually accomplishes, is simply better than inaction, than not doing anything at all, than never even beginning. How do we know? Because even keeping your own body alive would fail without action — that much wouldn't happen through doing nothing. And so the difference between action and inaction is plain for anyone to see in the world.
Close to the Sanskrit
Since thus, therefore —
'Prescribed' [means] constant, taught by scripture — whoever is entitled to whatever action, and [that action] not heard [i.e. not enjoined] for [any particular] fruit, that [is] prescribed action; that, perform, you, O Arjuna — because action [is] superior, more excellent, in terms of its fruit, than inaction — [i.e.] than non-doing, than non-undertaking. How [so]? Even the maintenance of the body, [i.e.] the continuance of the body, of you, would not be accomplished, would not be attained, from inaction, from non-doing. Therefore the distinction between action and inaction is observed in the world.