यदा हि नेन्द्रियार्थेषु न कर्मस्वनुषज्जते।
6.4 Verily, [Verily: This word emphasizes the fact that, since attachment to sense objects like sound etc. and to actions is an obstacle in the path of Yoga, therefore the removal of that obstruction is the means to its attainment.] when a man who has given up thought about everything does not get attached to sense-objects or acitons, he is then said to be established in Yoga.
6.4 When this Yogin, because of his natural disposition to the experience of the self, loses attachment, i.e., gets detached from sense-objects, i.e., things other than the self, and actions associated with them - then he has abandoned all desires and is said to have climbed the heights of Yoga. Therefore, for one wishing to climb to Yoga, but is still disposed to the experience of the sense-objects, Karma Yoga consisting of the practice of detachment to these objects, becomes the cause for success in Yoga. Therefore one who wishes to climb to Yoga must perform Karma Yoga consisting in the practice of detachment from sense-objects. Sri Krsna further elucidates the same:
Yadaa hi nendriyaartheshu na karmaswanushajjate; Sarvasankalpasannyaasee yogaaroodhas tadochyate.
yadā—when; hi—certainly; na—not; indriya-artheṣhu—for sense-objects; na—not; karmasu—to actions; anuṣhajjate—is attachment; sarva-saṅkalpa—all desires for the fruits of actions; sanyāsī—renouncer; yoga-ārūḍhaḥ—elevated in the science of Yog; tadā—at that time; uchyate—is said