In plain words
The Vedas deal with the three guṇas; rise beyond the three guṇas, Arjuna. Be free from the pairs of opposites, ever established in sattva, unconcerned with acquisition and preservation, and self-possessed.
Word for word
The Vedas have the three guṇas as their sphere; be beyond the three guṇas, O Arjuna, free of the pairs, ever abiding in sattva, free of [care for] acquiring and keeping, self-possessed.
The commentators
Bhagavadgītābhāṣyam
ये एवं विवेकबुद्धिरहिताः तेषां कामात्मनां यत् फलं तदाह —
त्रैगुण्यविषयाः त्रैगुण्यं संसारो विषयः प्रकाशयितव्यः येषां ते वेदाः त्रैगुण्यविषयाः । त्वं तु निस्त्रैगुण्यो भव अर्जुन, निष्कामो भव इत्यर्थः । निर्द्वन्द्वः सुखदुःखहेतू सप्रतिपक्षौ पदार्थौ द्वन्द्वशब्दवाच्यौ, ततः निर्गतः निर्द्वन्द्वो भव । नित्यसत्त्वस्थः सदा सत्त्वगुणाश्रितो भव । तथा निर्योगक्षेमः अनुपात्तस्य उपादानं योगः, उपात्तस्य रक्षणं क्षेमः, योगक्षेमप्रधानस्य श्रेयसि प्रवृत्तिर्दुष्करा इत्यतः निर्योगक्षेमो भव । आत्मवान् अप्रमत्तश्च भव । एष तव उपदेशः स्वधर्ममनुतिष्ठतः ॥ ४५ ॥
In plain words
Those who have no such discernment at all — people whose very self is desire — there is a result that comes to them, and that is what he says next:
'Having the three guṇas as their domain' simply means: the Vedas speak to the whole world of the three guṇas, to saṃsāra itself — that is their subject, that is what they expound. But you, Arjuna, rise above the three guṇas — be desireless, that's what it means. 'Free from the pairs of opposites' means: pleasure and pain, forever pulling against each other, are exactly what the word 'pair' refers to — stand clear of them, be free of every such pair. 'Ever grounded in sattva' means simply: rest always in the clarity of sattva. And likewise, 'free from acquisition and preservation' means: chasing after what you don't yet have is 'yoga' here, and guarding what you already have is 'kṣema' — and for anyone consumed by getting and keeping, real movement toward the highest good becomes almost impossible. So let go of that whole concern. And be self-possessed, and never careless. This, Arjuna, is the instruction for you, as you carry out your own dharma.
Close to the Sanskrit
Those who are thus devoid of discriminating intelligence — of them, whose very self is desire, whatever the fruit is, that he states —
'Having the three guṇas as their domain' [means]: the state of the three guṇas [is] saṃsāra, the topic to be expounded, of which they — the Vedas — [are] 'having the guṇa-world as their domain'. But you, be free from the three guṇas, Arjuna — [i.e.] be desireless — such is the meaning. 'Free from the pairs [of opposites]' [means]: pleasure and pain, the causes [of entanglement], mutually opposed entities, denoted by the word 'dvandva' — departed from those, be 'free from the pairs'. 'Ever grounded in sattva' [means]: always be resting on the guṇa of sattva. Likewise, 'free from [concern for] acquisition and preservation' [means]: the acquiring of what is not [yet] acquired [is] 'yoga' [in this sense]; the preserving of what has been acquired [is] 'kṣema'; for one for whom acquisition-and-preservation is paramount, engagement toward the highest good is difficult — therefore, be 'free from acquisition and preservation'. And be possessed of self and vigilant. This is the instruction for you, as one following his own dharma.