For the sage who wishes to climb to yoga, action is said to be the means; for that same person, once established in yoga, calm is said to be the means.
Explanation
Krishna is explaining to Arjuna how the path of yoga (spiritual discipline) develops in stages. For a beginner who wants to ascend, selfless action (karma) is the practice that trains the mind; for one already established, inner calm (śama) becomes the means of staying steady. Commentators differ on details: some read the 'calm' as renunciation of action, others as inner stillness while action continues.