This upanishad is based on atharva veda. It has total 7 kanDikaas.
rudra is one, past, present, future, soul of souls, all directions, eternal, mortal, expressed, concealed, brahman, non-brahman, male, female, neuter, all meters in poetry, all types of fires, truth, cow, gauri(his wife in worldly form), light, darkness, all vedas, eldest, respected, best, indestructible, destructible, pilgrim places, salubrious, sacred, eternal flame, energy.
Everything is within him – rudra.
Talks about eight planets. Mentions brahmaa, vishhNu being rudra.
Omkaara is praNava which is omnipresent. That omnipresent is flowing everywhere. That flows everywhere is subtle element. That subtle element is glowing and electrifying. That electrifying is parabrahma. parabrahma is one and that one is rudra.
Thus self consciousness, God’s consciousness and non-manifested consciousness above all are the same.
Omkaara is said thus because while pronouncing it, one has to bring breaths upward.
It is called praNava as it is used to bow down to ruk, yajuhu, atharva, angirasa and braahmaNas.
It pervades whole universe without being manifested, so it is called sarvavyaapi (omnipresent).
It is ananta (eternal) because there is no beginning or end while pronouncing it.
It is taaraka (savior) as it saves from fear of fetus, birth, aging, disease and death.
It is shukla (bright) as it is gives light to others.
It is called sookshma (subtle) as it becomes subtle after pronouncing it and remains in all bodies (physical, subtle, causal etc).
It is vidyuta (lightening) because it brightens all bodies even in darkness of ignorance.
It is called parabrahma as it expands para (non-manifested), apara (manifested) and paraayaNa (entangled).
It is brahman as it feeds on all lives and is ageless.
It is one and only one in all lives so it is called eka (one).
It is called rudra as it can be easily known by rushis (sages) and not by ordinary people.
It is called eeshaana (God) as it controls all energies and all devas (demi-Gods).
It is called maheshvara (supreme God).
rudra was manifested first.
If one attributes all accumulated deeds to rudra using intellect, s/he becomes one with paramaatman (supreme God).
The fourth half vowel in Omkaara is non-manifested form of all devas (demi Gods) and flows everywhere. It has pure crystalline form. Meditating upon its fourth half vowel sign brings liberation. This worship removes karmic bondage.
The whole world began from rudra that was in form of agni (fire).
rudra controls this whole world with dvidhaa (two – shiva and shakti) and tridhaa (three – sat, raja and tama). shakti is energy. shiva is welfare. Thus, dvidhaa is duality of mind and energy. sat is truth and light. raja is small particles. tama is ignorance and darkness. Thus tridhaa is material world made up of light, particles and darkness.
One who worships rudra’s moordhaa (top of head) in form of praNava (Omkaara) can attain highest position of atharvaa.
kaala (time) is born from akshara (indestructible).
When rudra starts sleeping, everything is destroyed. When he breathes, tama (ignorance and darkness) is created. tama creates aapaha (basic active element). Then rudra churns aapaha with finger so it coagulates. Further churning it, creates feeNa (foam). Foam creates brahmaanDa (cosmic egg). brahmaa comes into existence in that egg. brahmaa creates air. That air creates Omkaara. Omkaara creates saavitree (rays or waves). saavitree creates gaayatree (matter) and gaayatree creates animals.
One who reads atharvashira upanishad once, becomes pure and can attain welfare. Reading twice, one becomes ruler of humans. Reading thrice, one enters Omkaara which is in form of satya (truth) which is the only truth.