This 'Eternal Citta' is not-thought, not- created, not-penetrated, not-discribed, is pure, is enlighted, is the base of all, this Eternal Citta is the nature of all Dhamma, like a 0 is nature of all number.
When Ajhan Mun or others teachers say the word MIND, they dont mean the ordinary mind, they mean the nature of mind. So is not the Citta that eternal, but the Nature of Citta is eternal. Why it's eternal? Becase it's not-created. Like a canvas that not-painted, like a ground that not-build, like a silience that not-told...
In the sentence 'Eternal Citta', that is MOST important, is not 'Citta', but 'Eternal'. Ajhan Mun discribe that is Eternal but your mind associate on it the concept of Citta. Be careful.
If i will discribe Eternal Chair, or Eternal Table or Eternal Spoon, the discription of it will be the same that the 'Eternal Citta', why? Because 'Eternal'.
Eternity is Infinity, in all directions (space, time etc), there is can not be TWO Eternity. So by discribing a Eternal Spoon i will discribe the Eternal Citta at the same moment. Why? Because in this sentence, 'Eternal' is the quality, nature of statement. And Citta is the noun, is the atta, is the concept, mental form etc. Atta, form, concept must be rejecter, and you must hold only the quality, only the nature, only the Heart of one fenomena.
When you will see dhammas by they nature, see their kamma, and not by they name-and-form, you will see that Eternal Spoon is the heart of all buddhist practice and that Eternal Spoon is a right view, it not any dhamma but The Dhamma.
Just keep practice
Try to find this Eternal, Pure, Clear, Not-conditioned Spoon in your mind.