In plain words
But what need have you, Arjuna, to know all this in detail? Sustaining this entire universe with one fragment of Myself, I remain.
Word for word
Or else, what [use] for you is this much knowing, O Arjuna? Having upheld this whole world with one part, I stand.
अथवा बहुनैतेन किं ज्ञातेन तवार्जुनविष्टभ्याहमिदं कृत्स्नमेकांशेन स्थितो जगत्
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam· bhāṣya
अथवा बहुना एतेन एवमादिना किं ज्ञातेन तव अर्जुन स्यात् सावशेषेण । अशेषतः त्वम् उच्यमानम् अर्थं शृणु — विष्टभ्य विशेषतः स्तम्भनं दृढं कृत्वा इदं कृत्स्नं जगत् एकांशेन एकावयवेन एकपादेन, सर्वभूतस्वरूपेण इत्येतत् ; तथा च मन्त्रवर्णः — ‘पादोऽस्य विश्वा भूतानि’(ऋ. १० । ८ । ९० । ३) इति ; स्थितः अहम् इति ॥ ४२ ॥
In plain words
Or rather — what good would it really do you, Arjuna, to know all this only in part? Listen instead to the whole of what I am about to tell you. I stand, pervading and firmly upholding this entire world with a single portion of myself — one mere quarter — that is, in the very form of all beings. This is exactly what the Vedic verse itself says: 'A quarter of Him is all these beings.' That is how I stand.
Close to the Sanskrit
Or, what would be gained by you, Arjuna, from knowing this and the like at length, only partially? Listen to the topic being told to you completely — having pervaded, particularly having made a firm support of, this entire world with one part, one member, one quarter — that is, in the very form of all beings; this is that. And thus the Vedic text says — 'A quarter of Him is all these beings' (Ṛgveda 10.8.90.3) — thus; I am situated so — thus.