Millions of Indians chant the Shāntī Pāth or the peace invocation daily at the beginning and end of every satsangh, literally a gathering of truth-seekers. Such gatherings are commonplace among the populace where thousands assemble to listen to vedic discourses from Gurus of their choice. The Shāntī Pāth is placed at the beginning of the Iśavāsya Upanishad and in its extended form is the first shlöka of the 5^th Adhyāy of the Brihadaranayak Upanishad .

pūrnam adah, pūrnam idam, pūrnāt pūrnam udacyate
pūrnasya pūrnam ādāya pūrnam evāvaśisyate.

For our purpose here we take S.Radhakrishnan’s[1] explanation :
That is full, this is full. From fullness fullness proceeds.
If we take away the fullness of fullness, even then fullness remains.
Aum (the syllable) is Brahman (who) is the ether, the primeval ether….

Swami Chinmayanandji[2] explains it as follows :
That is Whole; this is whole; from the Whole the whole becomes manifest.
From the Whole when the whole is negated what remains is again the Whole.

Paul Deussen[3] translates it as:
That is perfect and this is perfect, out of the perfect, the perfect one is created.
If one takes out the perfect from the perfect, there still remains the perfect.
Om ! the expanse is Brahman, the wide expanse; the primaeval airspace filled with expanse !….

‘The Brhadāranyaka Upanisad’ by Ramakrishna Math is more explicit in its translation:
Om That (Brahman) is Infinite, this (universe) too is infinite. The infinite (universe) emanates from the Infinite (Brahman).
Assimilating the infinitude of the infinite (universe), the Infinite (Brahman) alone is left.
Om is the ether-Brahman – the ether that is eternal….

The word pūrna [4] has been variously translated above as full, whole, perfect and infinite. pūrna = pūr + kta[5] here pūr is the root that signifies fullness or completeness; the suffix kta is used to further stress this completion. In other words pūrna stands for something that is more than complete or beyond are imagination!