In plain words
There, making the mind one-pointed and restraining the activity of mind and senses, seated on the seat, one should practice yoga for purification of the inner being.
Word for word
There, having made the mind one-pointed, with the activities of mind and senses restrained, having sat on the seat, one should practise yoga for the purification of the inner faculty.
तत्रैकाग्रं मनः कृत्वा यतचित्तेन्द्रियक्रियःउपविश्याऽऽसने युञ्ज्याद् योगमात्मविशुद्धये
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam
प्रतिष्ठाप्य, किम् ? —
तत्र तस्मिन् आसने उपविश्य योगं युञ्ज्यात् । कथम् ? सर्वविषयेभ्यः उपसंहृत्य एकाग्रं मनः कृत्वा यतचित्तेन्द्रियक्रियः चित्तं च इन्द्रियाणि च चित्तेन्द्रियाणि तेषां क्रियाः संयता यस्य सः यतचित्तेन्द्रियक्रियः । स किमर्थं योगं युञ्ज्यात् इत्याह — आत्मविशुद्धये अन्तःकरणस्य विशुद्ध्यर्थमित्येतत् ॥ १२ ॥
In plain words
"Having established" — established what?
'There' means on that seat: sit down there and take up yoga. How? Withdraw from all objects, make the mind one-pointed, and hold the activities of mind and senses in check. Citta and the senses together are cittendriyāṇi; the one whose activities of these are restrained is yatacittendriyakriyaḥ. And for what purpose should he take up yoga? The verse answers: ātmaviśuddhaye, for self-purification — meaning, for the purification of the inner instrument, the antaḥkaraṇa.
Close to the Sanskrit
Having established — what?
'There' — that is, on that seat, having sat down, he should practise yoga. How? Having withdrawn from all objects, having made the mind one-pointed, being one whose mind-and-sense activities are restrained: citta and the senses are cittendriyāṇi; he whose activities of these are restrained is yatacittendriyakriyaḥ. For what purpose should he practise yoga? He says — 'for self-purification', which means: for the purpose of the purification of the inner instrument.