Buddhi is a 6 letter English word.
You can make 43 anagrams from letters in buddhi (bddhiu).
Sanskrit; compare bodhati (he) awakes
buddhi, though meaning intellect, is used rather in the sense of ascertaining or perception.
Human evolution develops the mental principle, Manas; Super-human evolution develops the spiritual body, buddhi.
Now, in the first place, nothing in the context warrants the explanation of the first 'tat' by buddhi.
Hence we conclude that the buddhi and the individual soul are spoken of.