Devi Parvati in worship of her Lord Shiva did the most incredible and Flawless selfless Tapasya.

Devi Parvati in worship of her Lord Shiva did the most incredible and Flawless selfless Tapasya.
At the culmination, she realised she is non separate from Him, such realisation is called SATCHITANANDA:
What this darkness,
what this light?
Plays of passion,
and what, is right?
breathing betwixt duality and pairs,
what,
she broods, is this maze?
earthgrown and foot firm
mindful yet, of above, beyond,
and
inner gaze.
Who am I ?
It intensifies.
In such stillness,
comes the flight,
who am I ?
Satchitananda,
I am even the sky !

{Adapted from Naam Roop A -Tribute to the Divine, by shail gulhati}