ॐ पूर्णमदः पूर्णमिदं पूर्णात्पुर्णमुदच्यते
पूर्णश्य पूर्णमादाय पूर्णमेवावशिष्यते ॥ॐ शान्तिः शान्तिः शान्त
This is the MANTRA in the ISHAVASHY UPANISHADA. The meaning of this is done by many and it differs and it causes the confusion . The meaning is THAT IS COMPLETE (OR INFINITE)ANDTHIS IS COMPLETE AND THIS COMPLETE COMES FROM THAT COMPLETE AND THAT COMPLETE CONTINUES TO BE COMPLETE
The confusion or question is , what is THAT and what is THIS . and everyone has their opinion And then how can complete remain complete when you take out complete. The answer is the way we consider origin of universe
I think THAT is BRAHMAN and THIS is the UNIVERSE which includes living and nonliving things, Known and UNKNOWN things The BRHAMAN is infinite and complete is very well known. It is described as STYAM , DNYANAM, ANANTAM . The meaning of ANATAM is - one which does not have end or one which is INFINITE.As we have talked everything that we SEE has 3 limitations, namely DESH-KAAL -VASTU ,meaning PLACE - TIME AND IDENTITY. But the BRAHAMN does not have this limitation and is limitless in space and time. So this Mantra states that THAT which is complete THIS world which is complete comes out .But THAT complete REMAINS COMPLETE.
The entire univers - seen and unseen comes out of the BRAHMAN. One can state this in many different ways . One can give example of DREAM WORLD . The dream world -may contain people , at different places and and may have animals , plants and nonliving things - but all COME OUT OF THE DREAMER and the dreamer is not reduced and has no loss .The dreamer continues to be COMPLTE as he was before he had dream. The same way the BRAHMAN continues to be COMPLETE or INFINITE even after THIS UNIVERSE comes out of it.