Sri Devi Atharva Shirsha, also called Devyupanishad, is a part of Atharvana Veda. Here is a brief translation of this great Upanishad.
"OM, all the Devas (celestials) approached Sridevi and asked her politely, "Great goddess (Mahadevi)! Who are you? What is your actual form?"
Sridevi answered thus, "I am indeed the supreme Parabrahman (my form is the same as that of Brahman). I emanate this world, composed of Prakriti and Purusha. I am the Shoonya (nothingness) and beyond the Shoonya. This world is both `Sat' (existent or true) as well as `Asat' (non-existent or false). I am both `Ananda' (bliss) and `Anananda' (misery). I am both `Vijnana' (science or right knowledge) as well as `Avijnana' (ignorance). I am the one who is recognized as Brahman and also as not Brahman or I am the Brahman that everyone should know and also the illusion. I am both Panchikrita as well as Apanchikrita Mahabhoota (I am of the form of all the elementals like air, water etc. as well as non-elementals), I am the entire visible world!"
In this way, Sridevi is describing her incomprehensible form in order to destroy the ignorance of her devotees (Devas), who are Mumukshus (have a desire to know her original form). One has to understand that if anything exists, its `her'. There is nothing that is existent other than Sridevi. She is the only ultimate truth.
"I wander in the form of Rudras and Vasus (a class of deities who are eight in number). I also roam in the form of Adityas and Vishwe Devas. I nurture (protect) Mitra, Varuna, Indra, Agni and Ashwini Devas. I hold Devas like Soma, Tvashta, Poosha and Bhaga in me (i.e. I appear in their form or they reside in me). I bear within myself, Brahma, Prajapati and Mahavishnu (whose gigantic feet transverse the three worlds)".
"I grant the sacred Havis to the Devas. I grant immense wealth (the greatest wealth being Sridevi herself!) to Yajamana (the one who performs Yagna and generates Soma Rasa thereby). I am the supreme Ishwari of this entire creation; I am the great Parabrahman, who grants wealth and prosperity to Upasakas. I am the chief (most important) among the Devas, who are eligible for accepting Havis in Yajnas. I am of the form of atman and from me are created the skies. My residence is in the intellect that recognizes the Self as Atman (Paramatman) (i.e. my place is in the intellect that is enlightened with the light of Atman). A person who understands this shall acquire divine wealth".
Sridevi here mentions the importance of Vedic Yagnas in achieving Moksha. She also describes that she is the one who grants Havis to the Devas and she is the one who receives it in the form of various Devas. She is the Yajamana as well as the Yagna. She also confers wealth and prosperity as well as Moksha to those who understand her form as being non-different from oneself i.e. as one's own Atman or as the Paramatman. Also here, `Paramanu Vada' is completely rejected. It is Sridevi who is the nucleus of the entire cosmos. She is also the nucleus in every minute cell. It is this Parabrahman who is in charge of the Paramanu.
Having understood Sridevi as their own self, as being non-different from the entire universe, as the sole existing entity, as the only truth, the Devas now pray: "O goddess, o great goddess! O auspicious Devi, o primordial nature, o granter of auspicious boons, we bow down to you repeatedly and regularly. Having a fire-like golden luster, Sridevi is shining due to austerities (here `Tapas' should be read to mean Jnana or knowledge). She has extraordinary brilliance. Every one bows down to this great goddess Durga for obtaining the fruits of the actions they have performed. Let us all seek refuge in Sri Durga Parameshwari, who destroys great demons".
Here, the Sruti refutes the claim of Mimamsa. It has to be understood that it is Sridevi or Brahman, who grants fruits for the actions or Yajnas performed. There is nothing called `Adrishta' that automatically assigns fruits for every mechanical action performed. Also, Sridevi is indicated here to be the very embodiment of Jnana. What she gives as a result to the actions performed? Herself and she is Brahma Vidya or Brahma Jnana. Thus, the purpose of every karma is obtaining Jnana – of the self, of Sridevi.
"Devas (i.e. Prana Vayu) created Vaikhari (audible speech) and living beings communicate through this Vaikhari. May that great goddess who resides in all beings as the power of speech, who is like the wish-fulfilling cow Kamadhenu, who grants bliss, who grants nutrition and strength through food and who is of the form of divine Paraa speech (which is subtle and beyond Vaikhari) come to us, pleased with our prayers".
"Let us bow down to Kalaratri (who is the destroyer of even Kala – Yama i.e. who is beyond the limitation of time), to the great goddess, who is praised by Brahma (i.e. the Vedas), who is the power of Vishnu and who is the mother of Skanda or Kartikeya (i.e. symbolizes Shiva-Shakti undifferentiated form), who is Saraswati – Brahma's creative power, who is Aditi, the mother of all Devas, who took birth as Dakshayani – Daksha's daughter, who is sanctifying and who grants auspicious boons".
"We meditate and invoke the great Mahalakshmi, who is the personification of all Shaktis, so that she may lead us to Jnana and Dhyana".
"O Daksha! From your daughter Aditi, the deathless Devas, who grant auspicious boons, originated".
Now the highly secretive Srividya Panchadashi Mahamantra is illustrated. I shall omit this since this has to be learnt from a guru.
"This great Vidya, which fulfills the desires of all beings, is the primary or the primordial Vidya of Sri Parashakti. This Vidya indeed is the Shakti of Parabrahman or atman (i.e. it is nothing but Brahma Vidya). It charms the entire universe with its brilliance. This great Sri Mahavidya pertains to Sri Lalita Mahatripurasundari who shines with noose, goad, bow and arrows in her hands. This Vidya indeed is the Veda. One who knows and understands this shall escape misery (of duality and ignorance)".
In this way, the Upanishad first gives out the Rahasya mantra in a code and then describes that this Vidya pertains to Sri Parashakti, who is none but the supreme formless Parabrahman. However, for the less advanced aspirant, it also gives out the Saguna meditation form describing the Lalita or Mahatripurasundari aspect of Sri Parashakti - Parabrahman. It is also declared that this Vidya is the essence of all the Vedas. One, who understands this, will become the knower of Brahma Vidya and shall thus escape from all bondages and attain liberation. Great scholars have also traced the meaning of this great Mahamantra in this Upanishad. It can be briefly summarized as follows:
"Mahatripurasundari is Shiva-Shakti Abheda Roopini (Shiva-Shakti one, without any difference), the congregation of Brahma, Vishnu and Shiva, the aggregation of Lakshmi, Saraswati and Gauri, she is approachable through Shuddha, Ashuddha and Mishra (pure, impure and a mixture of the two) Upasanas (depending on the eligibility and capacity of the Sadhaka), she is Nirvikalpa Jnana Swaroopini (Sridevi is pure consciousness) and is the essence of all Tatvas".
"O mother, we bow down to you, please protect us on all sides, in all ways. This great goddess appears as eight Vasus. She herself is the eleven Rudras, twelve Adityas, Vishwe Devas – both eligible for drinking Soma and otherwise too (i.e. she is in the form of Devas both eligible and ineligible for accepting Havis), Yatudhanas (a demon like race), Rakshas, Pishachas, Yakshas and Siddhas. She is of the form of Satva-rajas-Tamas, she is Brahma-Vishnu and Rudra, and she is Prajapati, Indra and Manu. She is the planets and stars. She indeed is Kalaa, kaashtaa and other units of time (i.e. she is time). we bow to this Mahadevi who is eternal".
The beauty of this Upanishad is that it establishes in every possible way, the Swaroopa of Sri Parashakti as being non-different from Parabrahman.
"I am Veda as well as anything that is not Veda (I am described by the Vedas, but I am not totally graspable even by the Vedas), I am Vidya as well as Avidya (knowledge as well as ignorance), I am the begginningless Prakriti and anything other than Prakriti (or I am the begginningless Maya as well as anything that is there apart from Maya). Down, above, left, right – every direction is pervaded by me!"
"We salute to her, who is the destroyer of sins, who grants both Bhoga (enjoyment) and Moksha, who is endless or infinite, who is ever victorious, who is pure, refuge of all beings, who grants auspiciousness and who is Brahman (Shiva represents Brahman)."
In the next verse, the Upanishad gives out Devi Pranava Mahamantra. "The Matrika letter `ha' represents Viyat, which means `Sky'. With a combination of `ii' kaara, it becomes `hii'. Viitihotra means Agni and is represented by the letter `ra'. Ardhendu means bindu. Thus, the mantra becomes `Hriim'. This mantra grants all desires. This mantra of single letter is Parabrahman i.e. it is the Akshara form of Brahman. Sages with pure consciousness, dive into the ocean of knowledge and experience supreme bliss by meditating on this Mahamantra".
The letter `ham' denotes Sadashiva Tatva. It is an aggregation of Shiva, Vishnu and Brahma Swaroopas. Thus, Sridevi is of the form of the Iccha – Jnana – Kriya triad. Also, since Sadashiva Tatva hints at Shiva – Shakti Samarasya, she is `Shiva- Shakti- one'. Letter `Ra' denotes `SphuraNa'. Thus, by the knowledge of Shiva – Shakti Aikya (i.e. the unity of Jiva and Parabrahman), the Chaitanya Shakti of Sridevi or Sri Kameshwara flows.
An alternate explanation would be: by understanding Shiva – Shakti Aikya (i.e. the unity of Jiva and Parabrahman), one burns or dissolves all Tatvas (i.e. gets rid of Satva, Rajas and Tamas). Then what? Next is `ii' – the Kamakala Akshara. It represents bliss. However, with Bindu, it becomes `iiM' and denotes Sat – chit – ananda. The letter has the same meaning as `Tat – Tvam – Asi'. Thus, by meditating on this Bija, one attains Sridevi who is Shiva – Shakti –one and who is of the form of sat – chit – ananda. Now, these are the Lakshanas of Parabrahman right! Thus, this mantra is also Brahma Vachaka at the same time. It is a pity people look down upon this Bija as `Tantrika Pranava'. Where `Aum' denotes the same Parabrahma Tatva, it speaks of Nishchala, Nirakara, Nirguna Tatva. Hrim also denotes the chit aspect of the same Parabrahma Tatva, with an added notion of `SphuraNa'.
Now, there is the uddhAra of navArNa Mahamantra.
"Vak is `Aim', Maya is `Hrim' and Brahmasuu (originated from Brahma i.e. Manmatha) is `Klim'. Then there is the sixth consonant (shashtham) along with `Vaktra' i.e. with `aa' kaara. Thus we get `chaa'. Surya is `ma'. `Avaama' is right and `Karna' is ear. Thus, the Nyasa letter for the right ear i.e. `u' with bindu is obtained. Together, it becomes `mu' with a bindu. The third letter from `Ta' is `Da' and along with Narayana (i.e. `aa') it becomes `Daa'. Vayu Bija is `Ya' and adharayuk (lower-lip, represented by `ai') together form `yai'. Add the word `Vicche' to these letters at the end. This nine-lettered Mahamantra grants extreme bliss to Sadhakas and also grants Brahma Sayujya".
The meaning of this mantra is as follows: O great mother Chamunda Durga, who is of the form of chit (Mahasaraswati), sat (Mahalakshmi) and Ananda (Mahakali), we meditate on you for obtaining Brahmavidya. Please sever the knots (Rajju Granthi) of Avidya and liberate us from duality. This Mahamantra thus, is also Brahma Vachaka. Next, the Saguna meditation of the mantra is illustrated.
"I bow down to Sridevi, who is seated in `Hrit Kamala' (heart lotus), who is bright like the rising sun, who is holding Pasha and Ankusha in her hands, who has a serene-beautiful form, who is three-eyed, who is wearing red garments and who grants all desires of her devotees. O mother, I salute to you, the great goddess, who destroys fear (the greatest fear being Bhava Bhaya), who removes the greatest of difficulties and who is the very personification of KaruNaa".
It is to be noted that the Dhyana here is actually of `Tripurasundari'. Thus, the claim that Sri Lalita Mahatripurasundari is the essence of seven crore mantras is supported even in the Sruti!
"Her form is unknown even to Brahma and the other Devas. Hence she is called `Ajneya' (impossible to be known as `this' or `that'). She is called `Ananta' because she is without any end. Since no one can see or identify her Lakshya (goal or gaze), she is `Alakshya'. No one knows of her birth and hence she is `Aja' – without birth i.e. begginningless. Since she exists everywhere, she is `Eka' – the one. But she is also the entire universe with its infinite forms of creation; thus she is also `Aneka' – many"
Here again, the Brahma swaroopa of Parameshwari is illustrated.
"I bow down to Sridevi who is present in all mantras as `Matrika' (i.e. the letters of the alphabet are her form and hence also the mantras which originate from these root letters), who is the meaning of every word (Shiva represents `Shabda' or word and Shakti its `Artha' or meaning. These two do not have a separate existence and this Avinabhava Sambandha is what is expressed here) and who is `Chinmayaateeta' (Jnana is through chit and Sridevi is even beyond chit (chit here should be taken to mean `Manas' or `Buddhi' i.e. mind or intellect. Sridevi represents the knowledge of Brahman, which cannot be grasped by mind or intellect. Also, she is above the planes of Manomaya and other Koshas). She is the silent witness of even Shoonya or `nothing'. It is this great goddess who is called Sri Durga and there is nothing existing beyond her (or she has no second)".
All these are again descriptions of the Vedanta Brahman. She is to be understood as the very Parabrahman or chit Parashakti. One of the many Pramanas could be her description as `silent witness'. This also speaks of `Kriya Shoonyata' of goddess. This is the concept of Brahman as accepted by Advaitins. This Upanishad beautifully expresses the same concept. Also, since she is the witness to `nothing' (which existed before everything and which shall exist after everything), she is the Anaadi Paramatman.
"Scared of the Samsara (duality), I salute to that Durga, who destroys the evil (durachara means anything that is unacceptable to Sruti and Smriti) and who takes us across the ocean of Samsara".
"One who studies (shravaNa, manana, dhyana and Sankirtana – listen, understand its meaning, contemplate on its purport and then chant the hymn) this Upanishad obtains the merit of chanting five other (Ganesha, Vishnu, Shiva etc.) Atharvopanishads. One who performs actions like worship, Pratimaa Sthaapana (installing an idol for ritualistic worship) without knowing this Upanishad will not get Siddhi even after chanting his a hundred lakh times! The Purashcharana prescribed for this hymn is 108. By chanting this hymn (after the Purashcharana. all the fruits described hereafter require purashcharana) ten times, one gets rid of all sins. By Sridevi's grace, one escapes from the greatest of difficulties. By chanting this hymn in the evening, one gets rid of the sins committed during the day. By chanting this hymn in the morning, one gets rid of the sins committed during the previous night. By using this hymn in the morning and evening (everyday) one becomes free from all sins. By chanting this during the Turiya Sandhya (midnight when Turiya meets Turiyatita), one gets Vak Siddhi. By chanting this hymn, Devata Saanidhya (presence of divinity) is accomplished in a new idol. By chanting this mantra during Bhaumashwini yoga (this could mean on a Tuesday with Ashwini Nakshatra or more appropriately during Amrita Siddhi Yoga), one escapes from the great death (untimely as well as timely!). In this way this Upanishad is Avidya Nashini and Brahma Pratipadini".