Bhashya
किं च यस्मिन् यत्र ब्रह्मणि, पञ्च पञ्चजनाः- गन्धर्वा-दयः पञ्चैव संख्याताः गन्धर्वाः पितरो देवा असुरा रक्षां-सि- निषादपञ्चमा वा वर्णाः, आकाशश्च अव्याकृताख्यः-यस्मिन् सूत्रम् ओतं च प्रोतं च- यस्मिन्प्रतिष्ठितः ; 'एत-स्मिन्नु खल्वक्षरे गार्ग्याकाशः' इत्युक्तम्; तमेव आत्मानम् अमृतं ब्रह्म मन्ये अहम्, न चाहमात्मानं ततोऽन्यत्वेन जाने ।किं तर्हि? अमृतोऽहम् ब्रह्म विद्वान्सन्; अज्ञानमात्रेण तु मर्त्योऽहम् आसम्; तदपगमात् विद्वानहम् अमृत एव ॥
In plain words
And 'in which' means in this very Brahman rest the five peoples — the Gandharvas and the rest, exactly five: Gandharvas, ancestors, gods, demons, and Rakshasas; or, by another count, the four castes with the Nishadas making a fifth. Space too — the unmanifest — rests here, the very space in which the fabric of existence is woven, thread by thread, crosswise and lengthwise. As it is said elsewhere: 'It is in this imperishable one, Gargi, that space itself is woven.' That alone — the self, the deathless Brahman — is what I hold myself to be; I know no self apart from it. What does that mean exactly? I am deathless, I am Brahman, and I know it; only through sheer ignorance was I ever mortal. Now that the ignorance is gone, I who know am nothing but deathless.
Close to the Sanskrit
Moreover, 'in which,' that is, in which Brahman — 'the five, the five classes of beings': Gandharvas and the rest, exactly five in number — Gandharvas, ancestors, gods, demons, Rakshasas; or, the castes with the Nishadas as a fifth; 'and space,' called the unmanifest, in which the thread is woven, both crosswise and lengthwise — 'in which it is established.' As it is said: 'in this very imperishable one indeed, O Gargi, is space woven, crosswise and lengthwise' — that alone, the self, the immortal Brahman, I regard; and I do not know the self as different from that. What then? I, knowing, am Brahman, immortal; but through mere ignorance I was mortal; with the removal of that ignorance, I, the knower, am indeed immortal.