In plain words
Transcending these three guṇas, from which the body arises, the embodied one is freed from birth, death, old age, and sorrow and attains immortality.
Word for word
Having passed beyond these three guṇas, the source of the body, the embodied one, freed from birth, death, old age and sorrows, attains immortality.
गुणानेतानतीत्य त्रीन् देही देहसमुद्भवान्जन्ममृत्युजरादुःखैर्विमुक्तोऽमृतमश्नुते
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam
कथम् अधिगच्छति इति, उच्यते —
गुणान् एतान् यथोक्तान् अतीत्य जीवन्नेव अतिक्रम्य मायोपाधिभूतान् त्रीन् देही देहसमुद्भवान् देहोत्पत्तिबीजभूतान् जन्ममृत्युजरादुःखैः जन्म च मृत्युश्च जरा च दुःखानि च जन्ममृत्युजरादुःखानि तैः जीवन्नेव विमुक्तः सन् विद्वान् अमृतम् अश्नुते, एवं मद्भावम् अधिगच्छति इत्यर्थः ॥ २० ॥
In plain words
So how does that actually happen? Here is the answer —
Having gone beyond these three guṇas already described, guṇas that are nothing but māyā's own conditioning, the very seed from which this body sprang, the embodied self breaks free while still alive from birth, death, old age, and every kind of suffering. Free like that while still living, the one who knows tastes what is deathless. And that, simply, is what it means to arrive at my own state.
Close to the Sanskrit
'How does one attain [it]?' — thus it is [now] explained —
Having transcended — while yet alive — having gone beyond these guṇas as already described, [which are] the limiting adjuncts of māyā, the three, born from the body, [i.e.] that have become the seed of the body's origination, the embodied one, by births, deaths, old age and sufferings — [namely] birth, and death, and old age, and sufferings — by those, being freed while yet alive, the knower tastes immortality: thus he attains My own state — this is the meaning.