In plain words
Attraction and aversion reside in the senses toward their respective objects. One should not come under their sway, for they are one's adversaries.
Word for word
Attraction and aversion are set in the object of each and every sense; one should not come under the sway of these two, for they are his adversaries.
The commentators
Bhagavadgītābhāṣyam
यदि सर्वो जन्तुः आत्मनः प्रकृतिसदृशमेव चेष्टते, न च प्रकृतिशून्यः कश्चित् अस्ति, ततः पुरुषकारस्य विषयानुपपत्तेः शास्त्रानर्थक्यप्राप्तौ इदमुच्यते —
इन्द्रियस्येन्द्रियस्य अर्थे सर्वेन्द्रियाणामर्थे शब्दादिविषये इष्टे रागः अनिष्टे द्वेषः इत्येवं प्रतीन्द्रियार्थं रागद्वेषौ अवश्यंभाविनौ तत्र अयं पुरुषकारस्य शास्त्रार्थस्य च विषय उच्यते । शास्त्रार्थे प्रवृत्तः पूर्वमेव रागद्वेषयोर्वशं नागच्छेत् । या हि पुरुषस्य प्रकृतिः सा रागद्वेषपुरःसरैव स्वकार्ये पुरुषं प्रवर्तयति । तदा स्वधर्मपरित्यागः परधर्मानुष्ठानं च भवति । यदा पुनः रागद्वेषौ तत्प्रतिपक्षेण नियमयति तदा शास्त्रदृष्टिरेव पुरुषः भवति, न प्रकृतिवशः । तस्मात् तयोः रागद्वेषयोः वशं न आगच्छेत् , यतः तौ हि अस्य पुरुषस्य परिपन्थिनौ श्रेयोमार्गस्य विघ्नकर्तारौ तस्करौ इव पथीत्यर्थः ॥ ३४ ॥
In plain words
If every living being acts only along the grain of its own inborn nature, and nobody is without such a nature, then human effort has nothing left to work on, and scripture is left with nothing to accomplish. It is to this that the following is said —
Wherever a sense meets its object, in whatever is pleasing, attachment arises; in whatever is unpleasant, aversion arises — this happens at every single sense-contact, and it happens whether you choose it or not. This is exactly where a person's own effort and scripture's guidance still have real work to do. So anyone taking up a scripturally guided life should be careful, right from the start, never to fall under the grip of attachment and aversion. Because a person's own nature, riding in on the back of exactly these two, will otherwise sweep them toward whatever nature wants — and that means abandoning the duty actually suited to them and picking up someone else's instead. But when a person holds attachment and aversion in check with a force that opposes them, scripture itself becomes their true guide, not their own unchecked nature. So never fall under the sway of these two. They are waylayers standing on your very own road to what is good for you — obstacles set right in your path, thieves lying in wait, exactly like bandits along the way.
Close to the Sanskrit
If every creature acts only in conformity with its own nature, and there is no one at all devoid of nature, then, since no sphere for human effort can be established, and scripture would thereby arrive at purposelessness, this is said —
In the object of each sense-organ, in the object of all the senses, in the object beginning with sound — in the desirable, attachment; in the undesirable, aversion: thus, with regard to every sense-object, attachment and aversion are bound to occur. In that connection, this is said to be the domain of human effort and of the purport of scripture. One engaged in scriptural duty should, beforehand, take care not to fall under the sway of attachment and aversion. For that nature which belongs to a person — that, preceded by attachment and aversion, impels the person toward its own proper function. Then abandonment of one's own duty and undertaking of another's duty occurs. But when, on the other hand, one restrains attachment and aversion by what opposes them, then the person becomes one whose guide is scripture, not one under the sway of nature. Therefore one should not fall under the sway of those two, attachment and aversion — because they are indeed waylayers of this person, makers of obstruction on the path to the highest good, like thieves on a road. That is the meaning.