In plain words
The state reached by the followers of Sāṅkhya is also reached by the yogins. One who sees Sāṅkhya and yoga as one truly sees.
Word for word
The state that is reached by the Sāṅkhyas, that is reached by the yogins also; who sees Sāṅkhya and yoga as one, he sees.
The commentators
Bhagavadgītābhāṣyam
एकस्यापि सम्यगनुष्ठानात् कथम् उभयोः फलं विन्दते इति उच्यते —
यत् साङ्ख्यैः ज्ञाननिष्ठैः संन्यासिभिः प्राप्यते स्थानं मोक्षाख्यम् , तत् योगैरपि ज्ञानप्राप्त्युपायत्वेन ईश्वरे समर्प्य कर्माणि आत्मनः फलम् अनभिसन्धाय अनुतिष्ठन्ति ये ते योगाः योगिनः तैरपि परमार्थज्ञानसंन्यासप्राप्तिद्वारेण गम्यते इत्यभिप्रायः । अतः एकं साङ्ख्यं च योगं च यः पश्यति फलैकत्वात् स पश्यति सम्यक् पश्यतीत्यर्थः — ॥ ५ ॥
In plain words
"If you practise only one of them, however rightly, how can you get the fruit of both?" To this it is said—
The same state called liberation, reached by the Sāṅkhyas — those renunciates fixed in knowledge — is reached by the yogins too: those who offer their actions to the Lord as a means to gaining knowledge, without seeking any fruit for themselves. They too reach that state, by way of finally attaining the renunciation that is knowledge of ultimate truth. That is the purport. So whoever sees Sāṅkhya and yoga as one, because their fruit is one and the same, that person truly sees — sees rightly. That is the meaning.
Close to the Sanskrit
"From the right performance of even one, how does one obtain the fruit of both?" — thus [the question]; it is answered —
The state called liberation which is attained by the Sāṅkhyas — those established in knowledge, the renunciates — that same state is also reached by the yogins: those who, having offered their actions to the Lord as a means of attaining knowledge, seeking no fruit for themselves, perform [action], are 'yogins.' By them too, that state is reached, through the gateway of attaining the renunciation that is knowledge of the highest truth — such is the purport. Therefore, he who sees Sāṅkhya and yoga as one, because of the oneness of their fruit, he sees; he sees correctly — this is the meaning.