The concept of the Vedantic mahavakya तत्त्वमसि is contained in the
Srividya Panchadashakshari mantra- कएईलह्रीं हसकहलह्रीं सकलह्रीं.
Let's see how.
तत्त्वमसि has three parts:तत्-त्वं-असि.
YOU-ARE-THAT.
YOU are what?
YOU are Brahman.
You are not different from Brahman, Parabrahma.
You are not different from God.
There is no duality.
Sadhana of Srividya Panchadashakshari mantra makes you realize this non-duality, attain this state of non-duality.
Just like how तत्त्वमसि has three parts, the Panchadashakshari mantra also has three parts called the three kutas, trikuta.
कएईलह्रीं
हसकहलह्रीं
सकलह्रीं
The first kuta stands for त्वं in तत्त्वमसि.
YOU in तत्त्वमसि.
There are five aksharas in the first kuta:
क-ए-ई-ल-ह्रीं
These aksharas have their own meaning.
क means born out of limitation or avidya imposed on Brahman.
This is what gives rise to the experience of THIS and THAT, YOU and I, I AM DIFFERENT FROM OTHERS, I AM A SEPARATE ENTITY.
This is because we are receiving information through the sensory organs which distort information and generate the sense of this duality.
Limitation or distortion of avidya imposed on the uniform homogenous Brahman.
Kakara stands for this concept.
ए in कएईलह्रीं means that you, Devi is above and beyond this distortion, this limitation.
Together ईल means, please remove.
ह्रीं- all sense of duality.
This sense of duality is त्वं, YOU as an individual, I as an individual,
feeling that YOU and I and THEY are all separate entities.
This Devi should remove, with all her kindness and blessings.
The second kuta हसकहलह्रीं stands for तत् in तत्त्वमसि.
तत् means- THAT.
The brahma-tattva, the parmatma-tattva, the parabrahma-tattva.
In the second kuta हसकहलह्रीं-
हस - please make me attain
क - Brahman
हल - all-pervading
ह्रीं - experience
Please make me attain the experience of the all-pervading Brahman; that Brahman is present in every single object and being in the universe.
Standng for तत्, Brahman in तत्त्वमसि.
The third kuta stands for असि in तत्त्वमसि.
सकलह्रीं - the experience of undivided oneness.
Here you also have to bring in हस from the previous kuta to understand the complete meaning.
Make me attain that experience of undivided oneness.
असि is the kriya-pada, the term signifying the action which can lead to the realization of this oneness between YOU and THAT which is sadhana with the mantra.
Ordinarily, you would always think in terms of duality or multiplicity.
But by doing sadhana of Srividya Panchadashakshari mantra, you would attain the experience of oneness.