6.12

तत्रैकाग्रं मनः कृत्वा यतचित्तेन्द्रियक्रियः ।
उपविश्यासने युञ्ज्याद्योगमात्मविशुद्धये ॥

tatraikāgraṃ manaḥ kṛtvā yatacittendriyakriyaḥ
upaviśyāsane yuñjyād yogam ātmaviśuddhaye

Kṛṣṇa (कृष्ण) is still speaking. The seat of 6.11 is tatra (तत्र), "there."

The verse

There, having made the mind one-pointed, having sat on the seat with the workings of mind and senses held in, he should yoke yoga for the cleansing of the self.

नेपालीमा

त्यहाँ मन एकाग्र पारेर, मन र इन्द्रियका क्रिया रोकेर आसनमा बसेर, उसले आत्माको शुद्धिका लागि योग जोड्नुपर्छ।

Where it sits

The seat now has a person on it, and the person has a reason. The yoga is for the cleansing of the self, not for a display of the seat.

Split: तत्र + एकाग्रम् + मनः + कृत्वा + यत-चित्त-इन्द्रिय-क्रियः + उपविश्य + आसने + युञ्ज्यात् + योगम् + आत्म-विशुद्धये

tatra + ekāgram + manaḥ + kṛtvā + yata-citta-indriya-kriyaḥ + upaviśya + āsane + yuñjyāt + yogam + ātma-viśuddhaye

Sanskrit, in depth

The words

देवनागरीWordGrammarSense
तत्रtatraindeclinablethere. On that seat.
एकाग्रम्ekāgramaccusative singularone-pointed. Agrees with manaḥ (मनः).
मनःmanaḥaccusative singularthe mind.
कृत्वाkṛtvāgerundhaving made.
यत-चित्त-इन्द्रिय-क्रियःyata-citta-indriya-kriyaḥnominative singularwhose activity of mind and senses is held in.
उपविश्यupaviśyagerundhaving sat down.
आसनेāsanelocative singularon the seat.
युञ्ज्यात्yuñjyātoptative, 3rd singularhe should yoke.
योगम्yogamaccusative singularyoga.
आत्म-विशुद्धयेātma-viśuddhayedative singularfor the cleansing of the self.

The phrases

tatra ekāgram manaḥ kṛtvā (तत्र एकाग्रम् मनः कृत्वा) is the mind, made one-pointed there. yatacittendriyakriyaḥ (यतचित्तेन्द्रियक्रियः) is the man while he does it: the workings of mind and senses are held.

upaviśya āsane (उपविश्य आसने) is the sitting down. युञ्ज्यात् योगम् आत्मविशुद्धये yuñjyāt yogam ātmaviśuddhaye is the purpose. He should yoke yoga, and the dative says what for: the cleansing of the self.

tatra ekāgram (तत्र एकाग्रम्) is tatraikāgram (तत्रैकाग्रम्). upaviśya āsane (उपविश्य आसने) is upaviśyāsane (उपविश्यासने). yuñjyāt yogam (युञ्ज्यात् योगम्) is yuñjyādyogam (युञ्ज्याद्योगम्), because t (त्) before a voiced sound is d (द्).

Sanskrit in this line

ātmaviśuddhaye (आत्मविशुद्धये) is dative, and the dative of an abstract noun often answers "what for." The ending --ye (ये) is the feminine द्-stem dative of viśuddhi (विशुद्धि), "cleansing." kṛtvā (कृत्वा) has no prefix, so it takes --tvā (त्वा). upaviśya (उपविश्य) has upa (उप), so it takes --ya (य). Same rule as 6.11.

Say it back

Mind, seat, and what the yoking is for. If ātmaviśuddhaye (आत्मविशुद्धये) comes out as "so that other people see him," stay here.