B.G 3.20

कर्मणैव हि संसिद्धिमास्थिता जनकादयः। लोकसङ्ग्रहमेवापि सम्पश्यन् कर्तुमर्हसि ॥२०॥

karmaṇaiva hi saṁsiddhimāsthitā janakādayaḥ। lōkasaṅgrahamēvāpi sampaśyan kartumarhasi ॥20॥

[कर्मणा एव हि संसिद्धिम् आस्थिता जनकादयः। लोकसङ्ग्रहम् एव अपि सम्पश्यन् कर्तुम् अर्हसि॥
karmaṇā = performing prescribed duties; ēva = alone; hi = indeed; saṁsiddhim = attain perfection; āsthitā = situated in that state; janakādayaḥ = King Janaka and others; lōkasaṅgraham = towards welfare of the world; ēva = alone; api = even; sampaśyan = having an eye; kartum = to act; arhasi = you are eligiable;]

Indeed, King Janaka and others could attain perfection and be in that state by performing prescribed duties alone. You are only eligible to perform your duties, having an eye towards the welfare of the world.

Gīta Tātparya 3.20

Sincerity towards attainment of knowledge is to perform activities as per the prescribed duties based on one's role in the society and phase of life. The ignorant must perform prescribed duties to gain knowledge. The knowledgeable must perform the prescribed duties for the welfare of the world.

सहैव कर्मणा सिद्धिमास्थिता जनकादयः। ज्ञाननिष्ठा अपि ततः कार्यं वर्णाश्रमोचितम्॥ इति च।

sahaiva karmaṇā siddhimāsthitā janakādayaḥ। jñānaniṣṭhā api tataḥ kāryaṁ varṇāśramōcitam॥ iti ca।

[sahaiva = by performing; karmaṇā = the duties; siddhimāsthitā = attained perfection;janakādayaḥ = King Janaka and the like; jñānaniṣṭhā = sincerity towards attainment of knowledge; api = is even; tataḥ = then; kāryaṁ = by performing activities; varṇāśramōcitam = as per the prescribed duties as per the phase of life and role in the society. iti ca = thus states the testimonial as well;]

King Janaka and others attained perfection by performing their respective duties. Therefore, sincerity towards attainment of knowledge is to perform activities as per the prescribed duties based on one's role in the society and phase of life (varna and ashrama). The testimonial also states the same:

अज्ञानां ज्ञानदं कर्म ज्ञानिनां लोकसङ्ग्रहात्। अद्धैव तुष्टिदं मह्यं सा मुक्तानन्दपूर्तिदा ॥२०॥

ajñānāṁ jñānadaṁ karma jñānināṁ lōkasaṅgrahāt। addhaiva tuṣṭidaṁ mahyaṁ sā muktānandapūrtidā ॥20॥

[ajñānāṁ = for the ignorant; jñānadaṁ = giver of knowledge; karma = the enjoyed duties; jñānināṁ = for the knowledgeable; lōkasaṅgrahāt = for the welfare of the world; addhaiva = immensely; tuṣṭidaṁ = satisfying; mahyaṁ = to me; sā = that; muktānandapūrtidā = giver of liberation, joy, and fulfillment;]

"For the ignorant prescribed duties result in knowledge. For the knowledgeable, it promotes the welfare of the world. It is the giver of liberation, joy, and fulfillment and is immensely satisfying to me."