This is the audio of our discussion of 2.21.

This aphorism (2.21) was discussed in Yogasūtra group in September 2017.

Sadāśivabrahmendra‘s Yogasudhākara commentary

(योगसुधाकर:)  इत्थं दृश्यद्रष्टारावभिधाय तयो: शेषशेषित्वमभिधातुमाह।
(Yogasudhākaraḥ) Ittham dṛśyadraṣṭāru abhidhāya śeṣaśeṣitvam abhdhatum āha.(Introduction to the sūtra) Thus defining the perceived and the perceiver, to express their object-subject connection he (Patañjali) says:

Sūtra 2.21

तदर्थ एव दृश्यस्यात्मा। (सू. २.२१) Tat-arthaḥ eva dṛśyasa ātmā. (2.21)
The essence of the perceived (world of objects) is only
for the sake of the perceiver (subject). (2.21)

(योगसुधाकर:) दृश्यस्य भोग्यस्यात्मा स्वरूपं द्रष्ट्रर्थमेव न स्वार्थमचेतनत्वादित्यर्थः।
(Yogasudhākaraḥ) dṛśyasya: bhogyasya, atmā: svarūpam, draṣṭṛ-artham eva na sva-artham acetantvāt iti arthaḥ
(Yogasudhākara commentary)The essence of the perceived is for the perceiver; not for its own sake, since it (the perceived, pradhāna) is insentient – this is meaning. 2.21.1

2.21.1 I use the word ‘perceived’ for dṛśya/pradhāna, this includes the phenomenal world as well as the body and mind of the perceiver (who is the seeker/ the liberated person). And, ‘ ‘perceiver’ is for dṛg/draṭṛ/puruṣa ).