In plain words
One who rejects the injunctions of śāstra and acts under the impulse of desire attains neither perfection, nor happiness, nor the supreme goal.
Word for word
Who, casting aside the injunction of śāstra, acts from the impulse of desire, he attains neither perfection, nor happiness, nor the supreme goal.
यः शास्त्रविधिमुत्सृज्य वर्तते कामकारतःन स सिद्धिमवाप्नोति न सुखं न परां गतिम्
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam
सर्वस्य एतस्य आसुरीसम्पत्परिवर्जनस्य श्रेयआचरणस्य च शास्त्रं कारणम् । शास्त्रप्रमाणात् उभयं शक्यं कर्तुम् , न अन्यथा । अतः —
यः शास्त्रविधिं शास्त्रं वेदः तस्य विधिं कर्तव्याकर्तव्यज्ञानकारणं विधिप्रतिषेधाख्यम् उत्सृज्य त्यक्त्वा वर्तते कामकारतः कामप्रयुक्तः सन् , न सः सिद्धिं पुरुषार्थयोग्यताम् अवाप्नोति, न अपि अस्मिन् लोके सुखं न अपि परां प्रकृष्टां गतिं स्वर्गं मोक्षं वा ॥ २३ ॥
In plain words
All of this rests on scripture: both the letting go of the āsurī sampat, the demonic endowment, and the actual practice of what is truly good. It is scripture's authority that makes both of them doable — there is no other way to it. And so —
Take the man in this verse. Śāstra here means the Veda, and its vidhi is its injunction — the one thing that lets you know what should be done and what should not, which is why it comes in two forms, precept and prohibition. He throws that injunction off; utsṛjya means exactly that, he drops it. And then he goes on living kāmakārataḥ — desire is what moves him. He does not reach siddhi, and siddhi means being fit even to pursue the goals a human life is for. He does not reach happiness here, in this world. And he does not reach the supreme destination — the highest there is, heaven or mokṣa.
Close to the Sanskrit
Of all this — of the abandoning of the demonic endowment and of the practice of the higher good — scripture is the cause. From the authority of scripture both are possible to do, not otherwise. Hence —
He who — śāstra means the Veda; its vidhi, the injunction, is the cause of the knowledge of what is to be done and what is not to be done, and goes by the name of precept and prohibition — casting off (utsṛjya, that is, abandoning) that scriptural injunction, proceeds kāmakārataḥ, being driven by desire: he does not attain siddhi, which means fitness for the goals of human life; nor even happiness in this world; nor even the supreme — that is, the highest — destination, whether heaven or liberation.