In plain words
Supreme happiness comes to the yogin whose mind is peaceful, whose rajas has quieted, who is free from impurity and has become Brahman.
Word for word
Indeed the highest happiness comes to this yogin whose mind is wholly calm, whose rajas is stilled, who has become Brahman, stainless.
प्रशान्तमनसं ह्येनं योगिनं सुखमुत्तमम्उपैति शान्तरजसं ब्रह्मभूतमकल्मषम्
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam· bhāṣya
प्रशान्तमनसं प्रकर्षेण शान्तं मनः यस्य सः प्रशान्तमनाः तं प्रशान्तमनसं हि एनं योगिनं सुखम् उत्तमं निरतिशयम् उपैति उपगच्छति शान्तरजसं प्रक्षीणमोहादिक्लेशरजसमित्यर्थः, ब्रह्मभूतं जीवन्मुक्तम् , ‘ब्रह्मैव सर्वम्’ इत्येवं निश्चयवन्तं ब्रह्मभूतम् अकल्मषं धर्माधर्मादिवर्जितम् ॥ २७ ॥
In plain words
*Praśāntamanasam* — a mind gone quiet, and *pra-* means all the way quiet: whoever has such a mind is *praśāntamanāḥ*, and it is him the verse points to. To this yogin comes the highest happiness — *uttama* here means *niratiśaya*, nothing above it, nothing further to reach for. It comes to him; it arrives. *Śāntarajasam* — the dust has settled: the dust that delusion and the other afflictions kick up has been worn away in him entirely. *Brahmabhūtam* — free while still alive, still breathing; a man in whom the certainty *Brahman alone is all* has set hard. That is what having become Brahman means. *Akalmaṣam* — not just washed clean of wrongdoing, but standing outside merit and demerit altogether.
Close to the Sanskrit
Praśāntamanasam: he whose mind is thoroughly stilled — pra-, to a high degree — he is praśāntamanāḥ; him, the one of thoroughly stilled mind. Indeed to this yogin the highest happiness — niratiśaya, that beyond which there is none — upaiti, comes, approaches. Śāntarajasam: the meaning is, one in whom the dust of the afflictions, delusion and the rest, has been wholly worn away. Brahmabhūtam: liberated while living; one who holds the settled certainty 'Brahman alone is all' — that is brahmabhūta. Akalmaṣam: free of merit and demerit and the rest.