In plain words
Because of delusion from the pairs of opposites, born from desire and aversion, Bharata, all beings fall into confusion at birth, scorcher of foes.
Word for word
By the delusion of the pairs, arising from desire and aversion, O Bhārata, all beings fall into bewilderment at birth, O scorcher of foes.
The commentators
Bhagavadgītābhāṣyam
केन पुनः मत्तत्त्ववेदनप्रतिबन्धेन प्रतिबद्धानि सन्ति जायमानानि सर्वभूतानि मां न विदन्ति इत्यपेक्षायामिदमाह —
इच्छाद्वेषसमुत्थेन इच्छा च द्वेषश्च इच्छाद्वेषौ ताभ्यां समुत्तिष्ठतीति इच्छाद्वेषसमुत्थः तेन इच्छाद्वेषसमुत्थेन । केनेति विशेषापेक्षायामिदमाह — द्वन्द्वमोहेन द्वन्द्वनिमित्तः मोहः द्वन्द्वमोहः तेन । तावेव इच्छाद्वेषौ शीतोष्णवत् परस्परविरुद्धौ सुखदुःखतद्धेतुविषयौ यथाकालं सर्वभूतैः सम्बध्यमानौ द्वन्द्वशब्देन अभिधीयेते । यत्र यदा इच्छाद्वेषौ सुखदुःखतद्धेतुसम्प्राप्त्या लब्धात्मकौ भवतः, तदा तौ सर्वभूतानां प्रज्ञायाः स्ववशापादनद्वारेण परमार्थात्मतत्त्वविषयज्ञानोत्पत्तिप्रतिबन्धकारणं मोहं जनयतः । न हि इच्छाद्वेषदोषवशीकृतचित्तस्य यथाभूतार्थविषयज्ञानमुत्पद्यते बहिरपि ; किमु वक्तव्यं ताभ्यामाविष्टबुद्धेः संमूढस्य प्रत्यगात्मनि बहुप्रतिबन्धे ज्ञानं नोत्पद्यत इति । अतः तेन इच्छाद्वेषसमुत्थेन द्वन्द्वमोहेन, भारत भरतान्वयज, सर्वभूतानि संमोहितानि सन्ति संमोहं संमूढतां सर्गे जन्मनि, उत्पत्तिकाले इत्येतत् , यान्ति गच्छन्ति हे परन्तप । मोहवशान्येव सर्वभूतानि जायमानानि जायन्ते इत्यभिप्रायः । यतः एवम् , अतः तेन द्वन्द्वमोहेन प्रतिबद्धप्रज्ञानानि सर्वभूतानि संमोहितानि मामात्मभूतं न जानन्ति ; अत एव आत्मभावे मां न भजन्ते ॥ २७ ॥
In plain words
But what exactly is in the way? By what obstruction to the knowing of My true nature are all beings held back, so that even as they come into birth they do not know Me? When that question is waiting to be asked, the Lord says this —
Desire and aversion — pull and push — rise up together, and it is from that pair that this delusion is born, Bhārata. Like heat and cold, they never stop opposing each other, always chasing what pleases and fleeing what pains, and they reach every living being in their own season — that is what 'the pair of opposites' means. The moment desire and aversion come fully into their own — the instant pleasure or pain, or whatever causes them, actually lands — they seize the discernment of that being and, holding it captive, breed the very delusion that blocks anyone from knowing the truth of the Self. A mind ruled by desire and aversion cannot even see an ordinary object clearly, so of course it cannot see something as deeply hidden as the innermost Self. This is why every being loses its bearings the instant it is born, scorcher of the foe — it arrives already confused. And because everyone's awareness is caught in this same delusion, no one recognizes Me as their own Self; and not recognizing this, no one worships Me as who they truly are.
Close to the Sanskrit
But by what obstruction to the knowing of My true nature, being obstructed, do all beings, as they are being born, not know Me? — when such a question is looked for, He says this —
By that which arises from desire and aversion: desire and hatred are 'desire-and-aversion'; that which arises from those two is 'arisen from desire-and-aversion'; by that, 'by that which arises from desire and aversion.' By what? — anticipating this need for specification, he says: 'by the delusion of the pair of opposites' — delusion whose cause is the pair of opposites is 'the delusion of the pair,' by that. Those very two, desire and aversion, like heat and cold, mutually opposed, having pleasure and pain and their causes as their objects, connecting with all beings according to occasion, are denoted by the word 'pair of opposites.' Where, when desire and aversion attain their full being through the arrival of pleasure, pain, and their causes, then those two, by bringing the discernment of all beings under their own control, produce delusion, which is the obstructing cause for the arising of knowledge of the truth of the supreme Self. For indeed, for one whose mind is overpowered by the fault of desire and aversion, knowledge of an object as it really is does not arise even outwardly; how much less need be said that, for one whose intellect is possessed by those two and utterly deluded, knowledge does not arise regarding the inner Self, which has many more obstructions. Therefore, by that delusion of the pair of opposites arisen from desire and aversion, O Bhārata — one born in the line of Bharata — all beings are deluded; they go to delusion, that is, to bewilderment, at 'creation,' at birth, at the time of origination — this is the sense; 'they go' means 'they proceed,' O scorcher of the foe. The intention is that all beings, as they are born, are born under the sway of delusion alone. Since this is so, therefore all beings, whose awareness is obstructed by that delusion of the pair of opposites, being deluded, do not know Me as their own Self; precisely for this reason they do not worship Me in the mode of the Self.