Bhashya
एवं तावच्चतुर्थोपनिषदि अन्ते मृत्युप-निषदा महाचक्रस्थद्वात्रिंशत्पत्रेषु य-थासंख्यं द्वात्रिंशन्नृसिंहमृत्युपाख्यान-भिधाय, अथेदानीं महाचक्रविद्याम-भिधातुं महाचक्रस्वरूप निरूपयितुंप्रश्नोत्तररूपाख्यायिकया पञ्चमोपनि-षदारभ्यते—देवा ह वै प्रजापतिमब्रुवन्निति ।नन्वेवं तर्हिस्तुत्युपनिषद्विद्यातो महाचक्रविद्यया प्राग्भावितव्यम् ।अत्रो-च्यते ।सत्यम् ।यदीयं प्राक्स्यात् पुरश्चरणार्थं पञ्चमाङ्गन्या-सार्थं च कृत्स्नैव प्रतीयेत ; न तु द्वात्रिंशद्व्यूहोपासनामात्रंपुरश्चरणार्थम् इतरत् सुदर्शनादिमहाचक्रं सहाद्वात्रिंशद्व्यूहकंपञ्चमाङ्गम् इत्येवं विभागः प्रतीयेत ।अतस्तद्विभागज्ञापनार्थंन प्रागभिहितेयमिति ।नन्वेवमपि तदादिन्यायेन महाचक्र-विद्या पुरश्चरणार्थं कृत्स्नैव कस्मान्न गृह्येत ।तन्न, तत्र तदा-दिन्यायवैषम्यात् ।न हि महाचक्रस्यायमादिर्द्वात्रिंशद्व्यूहो
In plain words
A bit of editorial bookkeeping, but a telling one: having spent the fourth section on thirty-two legends of Narasiṃha and death mapped onto the thirty-two petals of the Great Wheel, the text now turns to explain that Wheel itself, and does so as a fifth teaching, cast as a dialogue — the gods asking, Prajāpati answering. Someone objects: shouldn't this teaching about the Wheel have come before the eulogy that was just finished? Fair, comes the reply — but here's why it didn't. Had it come first, a reader would have assumed the whole Wheel-teaching was just preparation, just the placing of one ritual limb among five — as if worshipping the thirty-two emanations were the whole of it. Putting it here instead makes the real shape visible: the thirty-two-emanation wheel is only one part; Sudarśana and its companion wheels, taken together, form that fifth limb. Order, in other words, is doing teaching work, not just following a schedule. A second objection follows close behind: if 'whatever comes first sets the rule' is the principle, why not just take the entire Wheel-teaching as preparatory practice? Because, the text answers, that principle doesn't apply evenly here — this thirty-two-fold wheel is not actually the starting point of the Great Wheel...
Close to the Sanskrit
Thus, so far, at the end of the fourth Upaniṣad, by the Mṛtyu-Upaniṣad [section], having narrated, correspondingly, the thirty-two Narasiṃha-death legends situated on the thirty-two petals of the Great Wheel, now, in order to explain the teaching of the Great Wheel and to describe the nature of the Great Wheel, the fifth Upaniṣad begins by way of a question-and-answer narrative: 'The gods indeed said to Prajāpati' — thus. Now, if so, then, the Great-Wheel teaching ought to have come before the eulogy-Upaniṣad teaching. Here it is replied: true. If this [teaching] were placed earlier, it would be understood entirely as being for the purpose of preliminary practice and for the purpose of placing the fifth limb; but not [merely] the worship of the thirty-two emanations alone, for the purpose of preliminary practice — [rather] a division would be understood thus: the rest, the Sudarśana and other [wheels] of the Great Wheel together with the thirty-two-emanation wheel, is the fifth limb. Therefore, for the purpose of making that division known, this was not stated earlier. Now, even so, by that same maxim of what-comes-first, why should not the entire Great-Wheel teaching be taken as for the purpose of preliminary practice? That is not so; there, because the maxim of what-comes-first does not apply evenly. For this thirty-two-emanation [wheel] is not the beginning of the Great Wheel [continues]...