Rig veda 10.90.15

सप्तास्यासन् परिधयस् त्रिः सप्त समिधः कृताः |
देवा यद् यज्ञं तन्वाना अबध्नन् पुरुषम् पशुम् ||

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saptāsyāsan paridhayas triḥ sapta samidhaḥ kṛtāḥ |
devā yad yajñaṃ tanvānā abadhnan puruṣam paśum ||

- saptāsyāsan paridhayas  : Seven (physical-vital-mental-supermental-harmony-force-existence planes or bhu-bhuvar-svar-maha-jana-tapah-sat lokasabha) were the fencing sticks (that put the boundary around original purusha)

-  triḥ sapta samidhaḥ kṛtāḥ : three times seven = 21 ( seven planes acting in the three lower planes of physical-vital-mental) were the layers of fuel
- devā yad yajñaṃ : The devas (purusha in the seven planes who are aware of their divine origin) perform the sacrifice ( the continuous  act of creation)

- tanvānā abadhnan puruṣam paśum : by binding the purusha (in the three lower planes) as the (helpless) sacrificing the animal (by projecting the purusha in the seven planes and by making the projections forget it's divine origins)

21 layers of fuel are

1. Pure physical plane

2. Vital physical

3. Mental physical

4. Supermental physical

5. Harmony physical

6. Force physical

7. Existence physical

8. Physical vital

9. Pure vital

10. Mental vital

11. Supramental vital

12. Harmony vital

13. Force vital

14. Existence vital

15. Physical mental

16. Vital mental

17. Pure mental

18. Supramental mental

19. Harmony mental

20. Force mental

21. Existence mental

Rig veda 1.1.3

अग्निना रयिम् अश्नवत् पोषम् एव दिवे-दिवे |
यशसं वीरवत्तमम् ||

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agninā rayim aśnavat poṣam eva dive-dive |
yaśasaṃ vīravattamam ||

- agninā rayim aśnavat : By agni (soul) one obtains treasure (divine connection)

- poṣam eva dive-dive : that increases day by day 
- yaśasaṃ vīravattamam : which (this treasure of divine connection ) also gives hero's strength

Rig Veda 10.90.12

ब्राह्मणो ऽस्य मुखम् आसीद् बाहू राजन्यः कृतः |
ऊरू तद् अस्य यद् वैश्यः पद्भ्यां शूद्रो अजायत ||

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brāhmaṇo 'sya mukham āsīd bāhū rājanyaḥ kṛtaḥ |
ūrū tad asya yad vaiśyaḥ padbhyāṃ śūdro ajāyata ||

- brāhmaṇo 'sya mukham āsīd : Brahmin (associates with ) the face (which is the seat of mental being) of the purusha

- bāhū rājanyaḥ kṛtaḥ : Arms (the seat of upper vital or mental vital) of purusha is the warrior king (associates himself with)
- ūrū tad asya yad vaiśyaḥ : Thighs (the seat of lower vital or physical vital) of the purusha are the mercantile class (associating with)

- padbhyāṃ śūdro ajāyata : The feet (the seat of physical being) of the purusha are he workers (associating with)

Katha Upanishad 2.1.8

अरण्योर्निहितो जातवेदा गर्भ इव सुभृतो गर्भिणीभिः।
दिवे दिवे ईड्यो जागृवद्भिर्हविष्मद्भिर्मनुष्येभिरग्निः। एतद्वै तत्‌ ॥

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araṇyornihito jātavedā garbha iva subhṛto garbhiṇībhiḥ |
dive dive īḍyo jāgṛvadbhirhaviṣmadbhirmanuṣyebhiragniḥ | etadvai tat ||

- araṇyornihito jātavedā : In the forest (vital being behind heart) resides (hides) the knower of birth (our soul agni)

- garbha iva subhṛto garbhiṇībhiḥ : Like a pregnant woman (symbolic of the human physical-vital-mental being ) with care carries the womb (symbolic of the soul agni which is trying to take birth by expressing out from the mind-vital-physical being)

- dive dive īḍyo: Day by day (agni the soul) is worshipped by the

- jāgṛvadbhirhaviṣmadbhirmanuṣyebhiragniḥ : One who are in wakeful state (physical consciousness as against dream state of vital/mental consciousness or deep sleep state of supramental consciousness) , one (vital being) who desire to stand in front for performing sacrifice (with agni/soul as the priest connecting them to gods) and who are the men (mental beings)

- etadvai tat : this (agni/soul) is the one you are seeking.

Ishavasya upanishad verse 11

विद्याञ्चाविद्याञ्च यस्तद्वेदोभयं सह।
अविद्यया मृत्युं तीर्त्वा विद्ययाऽमृतमश्नुते ॥

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vidyāñcāvidyāñca yastadvedobhayaṁ saha |
avidyayā mṛtyuṁ tīrtvā vidyayā'mṛtamaśnute ||

- vidyāñcāvidyāñca yastadvedobhayaṁ saha : He who knows both the (spiritual transformation by) knowledge  and the (supramental transformation by entering the) ignorance together (as the same divine work)
- avidyayā mṛtyuṁ tīrtvā : crosses death (which is a challenge in lower hemisphere of mind-life-matter) by (supramental transformation of) ignorance and 

- vidyayā'mṛtamaśnute : Attains immortality (which is the nature of upper hemisphere of existence-force-harmony) by (spiritual transformation through) knowledge

Ishavasya Upanishad Verse 10

अन्यदेवाहुर्विद्ययाऽन्यदाहुरविद्यया।
इति शुश्रुम धीराणां ये नस्तद्विचचक्षिरे ॥

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anyadevāhurvidyayā'nyadāhuravidyayā |
iti śuśruma dhīrāṇāṁ ye nastadvicacakṣire ||

- anyadevāhurvidyay : Other (ie. spiritual Ascension transformation) verily comes from (the revelation of) the knowledge (of unity of atman and brahman consciousness)

- ā'nyadāhuravidyayā : Other (ie. Supramental  transformation)  verily comes from (descending into the) ignorance (  of the lower hemisphere of mind-life-matter and connecting it of the divine origin)
iti śuśruma dhīrāṇāṁ : This (wisdom) we have heard from the wise ones

ye nastadvicacakṣire : This had been revealed to our understanding

Ishavasya Upanishad verse 9

अन्धं तमः प्रविशन्ति येऽविद्यामुपासते।
ततो भूय इव ते तमो य उ विद्यायां रताः ॥

andhaṁ tamaḥ praviśanti ye'vidyāmupāsate |
tato bhūya iva te tamo ya u vidyāyāṁ ratāḥ ||

- andhaṁ tamaḥ praviśanti : Blind darkness (of lower hemisphere made of mind-life-matter which is cut off from knowledge of divine origin) does one enter

- ye'vidyāmupāsate : who pursues only the (supramental transformation which tries to descend into the) ignorance

- tato bhūya iva te tamo: Into a greater darkness ( of straying from the path of divine which is trying to transform the lower hemisphere) he enters

- ya u vidyāyāṁ ratāḥ: who pursues only the path of (ascending moksha that pursues the path of)  knowledge (of divine origin and higher hemisphere of existence-force-harmony while abandoning the lower hemisphere)