प्रवृत्तिंच निवृत्तिं च कार्याकार्ये भयाभये |
बन्धं मोक्षं च या वेत्तिबुद्धि: सा पार्थ सात्विकी ||

pravṛittiṁ cha nivṛittiṁ cha kāryākārye bhayābhaye
bandhaṁ mokṣhaṁ cha yā vetti buddhiḥ sā pārtha sāttvikī

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भावार्थ:

हे पार्थ ! जो बुद्धि प्रवृत्तिमार्ग (गृहस्थ में रहते हुए फल और आसक्ति को त्यागकर भगवदर्पण बुद्धि से केवल लोकशिक्षा के लिए राजा जनक की भाँति बरतने का नाम ‘प्रवृत्तिमार्ग’ है।) और निवृत्ति मार्ग को (देहाभिमान को त्यागकर केवल सच्चिदानंदघन परमात्मा में एकीभाव स्थित हुए श्री शुकदेवजी और सनकादिकों की भाँति संसार से उपराम होकर विचरने का नाम ‘निवृत्तिमार्ग’ है।), कर्तव्य और अकर्तव्य को, भय और अभय को तथा बंधन और मोक्ष को यथार्थ जानती है- वह बुद्धि सात्त्विकी है ॥

Translation

18.30 The intellect which knows the path of work and renunciation, what ought to be done and what ought not to be done, fear and fearlessness, bondage and liberation that intellect is Sattvic (pure), O Arjuna.

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English Translation Of Sri Shankaracharya’s Sanskrit Commentary By Swami Gambirananda

18.30 O Partha, sa, that; buddhih, intellect; is sattviki, born of sattva; ya, which; vetti, understands; pravrttim, action, the path of rites and duties, which is the cause of bondage; and nivrttim, withdrawal, the path of renunciation, which is the cause of Liberation-since action and withdrawal are mentioned in the same sentence along with bondage and freedom, therefore they mean ‘the path of rites and duties and of renunciation’-; karya-akarye, duty and what is not duty, i.e. what is enjoined or prohibited, [Ast. adds laukike vaidike va (ordinary or Vedic injunctions and prohibitions) after vihita-pratisiddhe; and it adds sastrabuddheh before kartavya-akartavye-what ougth to be done or ought not to be done by one who relies on the scriptures.-Tr.] what ought to be done or ought not to be done, action and inaction. With regard to what? With regard to action leading to seen or unseen, results, undertaken according to place, time, etc. Bhaya-adhaye, the sources of fear and fearlessness, i.e. the cuases of fear and fearlessness, with regard to seen or unseen objects; bandham, bondage, along with its cause; and moksam, freedom, along with its cause.

In this context, knowing is a function of the intellect; but the intellect is the possesser of the function. Fortitude also is only a particular function of the intellect.