In plain words
the sage who has mastered senses, manas, and buddhi, intent on Mokṣa and free from desire, fear, and anger, and who is always so, is free indeed.
Word for word
the muni whose senses, manas and buddhi are controlled, intent on mokṣa, from whom desire, fear and anger have gone, who is always [so], he is free indeed.
The commentators
Bhagavadgītābhāṣyam· bhāṣya
स्पर्शान् शब्दादीन् कृत्वा बहिः बाह्यान् — श्रोत्रादिद्वारेण अन्तः बुद्धौ प्रवेशिताः शब्दादयः विषयाः तान् अचिन्तयतः शब्दादयो बाह्या बहिरेव कृताः भवन्ति — तान् एवं बहिः कृत्वा चक्षुश्चैव अन्तरे भ्रुवोः ‘कृत्वा’ इति अनुषज्यते । तथा प्राणापानौ नासाभ्यन्तरचारिणौ समौ कृत्वा, यतेन्द्रियमनोबुद्धिः यतानि संयतानि इन्द्रियाणि मनः बुद्धिश्च यस्य सः यतेन्द्रियमनोबुद्धिः, मननात् मुनिः संन्यासी, मोक्षपरायणः एवं देहसंस्थानात् मोक्षपरायणः मोक्ष एव परम् अयनं परा गतिः यस्य सः अयं मोक्षपरायणो मुनिः भवेत् । विगतेच्छाभयक्रोधः इच्छा च भयं च क्रोधश्च इच्छाभयक्रोधाः ते विगताः यस्मात् सः विगतेच्छाभयक्रोधः, यः एवं वर्तते सदा संन्यासी, मुक्त एव सः न तस्य मोक्षायान्यः कर्तव्योऽस्ति ॥ २८ ॥
In plain words
'Having pushed the contacts outside' means sound and the rest, which are external, stay outside — for someone who no longer dwells on them, these sense-objects that had entered the intellect through the ear and the other senses simply remain outside, so to speak. 'Having made them so, and the eye too, fixed between the eyebrows' — 'having made' carries over from before. Likewise, 'having balanced the outgoing and downward breaths' moving within the nostrils. 'Whose senses, mind, and intellect are controlled' means exactly that — his senses, mind, and intellect are reined in and restrained. 'Muni' comes from reflecting, meaning a renunciant. 'Whose supreme resort is liberation' — held in this very bodily posture, he is someone for whom liberation, and nothing else, is the final destination; such a person, this muni whose only refuge is liberation, is what he should become. 'Free of desire, fear, and anger' means desire, fear, and anger have all left him. Whoever lives this way, always, is a true renunciant — he is already liberated. There is nothing more he needs to do to reach liberation.
Close to the Sanskrit
'Having made the contacts,' [i.e.] sound and the rest, [which are] 'external,' 'outside' — the sense-objects, sound and the rest, that have entered inward into the intellect through the channel of the ear and the other senses, for one who does not dwell on them, sound and the rest, being external, stay simply outside, so to speak — 'having made them thus outside, and the eye too, between the eyebrows' — 'having made' is carried over [from the earlier phrase]. Likewise, 'having made equal the outgoing and downward breaths,' [i.e.] moving within the nostrils — 'whose senses, mind, and intellect are controlled': [i.e.] the senses, mind, and intellect, controlled, [i.e.] restrained, of whom — he is 'one whose senses, mind, and intellect are controlled.' 'Muni,' from reflecting, [i.e.] a renunciant; 'having liberation as the supreme resort' — thus, by virtue of this bodily posture, he is 'one whose supreme resort is liberation'; liberation alone is the supreme resort, the supreme goal, of whom — he, this one whose supreme resort is liberation, should be a muni. 'Free of desire, fear, and anger' — desire and fear and anger, [together] 'desire-fear-anger,' those, having departed, from whom — he is 'free of desire, fear, and anger.' Whoever lives thus, always, is a renunciant; he is indeed liberated; for him there is nothing else to be done toward liberation.