In plain words
Therefore, mighty-armed one, one whose senses are completely restrained from their objects has wisdom firmly established.
Word for word
Therefore, O mighty-armed, whose senses are restrained on every side from the objects of the senses, his wisdom is firmly set.
The commentators
Bhagavadgītābhāṣyam
‘यततो हि’(भ. गी. २ । ६०) इत्युपन्यस्तस्यार्थस्य अनेकधा उपपत्तिमुक्त्वा तं चार्थमुपपाद्य उपसंहरति —
इन्द्रियाणां प्रवृत्तौ दोष उपपादितो यस्मात् , तस्मात् यस्य यतेः हे महाबाहो, निगृहीतानि सर्वशः सर्वप्रकारैः मानसादिभेदैः इन्द्रियाणि इन्द्रियार्थेभ्यः शब्दादिभ्यः तस्य प्रज्ञा प्रतिष्ठिता ॥ ६८ ॥
In plain words
Having argued, from several angles, for the point he first raised in 'even for one who strives...' (2.60), and having fully established it, Kṛṣṇa now brings it to a close —
Since the danger in letting the senses run loose has already been shown, therefore, mighty-armed one, whoever's senses have been restrained completely, through every method — mental control and the rest — away from their objects, from sound and everything like it, that person's wisdom stands firmly established.
Close to the Sanskrit
Having stated, in many ways, the proof of the point propounded [beginning] 'of one who strives, indeed' (Gītā 2.60), and having established that same point, he [now] concludes —
Since the fault in the engagement of the senses has been established, therefore, O mighty-armed one, the striver whose senses have been restrained completely, in every way, by every method, by distinctions such as the mental and so on, [restrained] from the objects of the senses, from sound and the rest — his wisdom is established. [End of commentary on verse 68.]