In plain words
And one who serves Me through unwavering Bhakti-yoga transcends these guṇas and becomes fit for becoming Brahman.
Word for word
And who serves Me with unswerving bhakti-yoga, he, having gone fully beyond these guṇas, is fit for becoming Brahman.
मां च योऽव्यभिचारेण भक्तियोगेन सेवतेस गुणान् समतीत्यैतान् ब्रह्मभूयाय कल्पते
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam
अधुना ‘कथं च त्रीन्गुणानतिवर्तते ? ’(भ. गी. १४ । २१) इत्यस्य प्रश्नस्य प्रतिवचनम् आह —
मां च ईश्वरं नारायणं सर्वभूतहृदयाश्रितं यो यतिः कर्मी वा अव्यभिचारेण न कदाचित् यो व्यभिचरति भक्तियोगेन भजनं भक्तिः सैव योगः तेन भक्तियोगेन सेवते, सः गुणान् समतीत्य एतान् यथोक्तान् ब्रह्मभूयाय, भवनं भूयः, ब्रह्मभूयाय ब्रह्मभवनाय मोक्षाय कल्पते समर्थो भवति इत्यर्थः ॥ २६ ॥
In plain words
Now for the answer to the question, 'And how does someone go beyond the three guṇas?' (Gītā 14.21). He replies:
Me — the Lord, Nārāyaṇa, who lives in the heart of every being — whether an ascetic or someone still caught up in action, whoever serves without ever once wavering, through the yoga of devotion (and devotion is exactly what that yoga is), that person, through such service, fully goes beyond these guṇas already described and becomes ready to become Brahman itself, ready, that is, for liberation. That's all this means: he becomes capable of it, and he arrives there.
Close to the Sanskrit
Now, of this question — 'And how does he transcend the three guṇas?' (Bhagavad Gītā 14.21) — he states the reply:
Me — the Lord, Nārāyaṇa, who dwells in the hearts of all beings — whichever ascetic or man of action, without deviation, never at any time, [i.e.] who does not deviate, serves by the yoga of devotion — 'bhajana' [means] devotion, that itself is 'yoga' — by that yoga of devotion he serves — he, having fully transcended these guṇas as already described, becomes fit for becoming Brahman — 'bhavana' [means] becoming; for becoming Brahman, [i.e.] for the state of becoming Brahman, for liberation, he becomes fit, [i.e.] capable: this is the meaning.