The epanalepsis is a figure of speech which consists in the repetition of the beginning word of a clause or sentence in the end. The beginning and the end are the two positions of stronger emphasis in a sentence so, by having the same word in both places, one calls special attention to it. A figure of speech, sometimes termed a rhetorical figure or device, or elocution, is a word or phrase that departs from straightforward, literal language. ... In grammar, a clause is a group of words consisting of a subject and a predicate, although, in non-finite clauses, the subject is often not explicitly given. ... The word emphasis, in addition to its main dictionary meaning, may have the following techincal meanings. ...
This technique is based upon a figure of speech which defines exactly what Bach is doing when he has the vocalist, at the conclusion of the aria, sing once again the opening words of the aria.
It would be stretching the meaning of epanalepsis to apply it to the numerous instances where Bach simple uses an echo effect, where the echo follows immediately upon the 1st statement.
Bach has been 'hammering this theme in' polyphonically to such a degree that there is no special emotional effect attached to the tromba's final entry, where the listener simply feels that this is a good place to stop.
Epanalepsis repeats the beginning word of a clause or sentence at the end.
The beginning and the end are the two positions of strongest emphasis in a sentence, so by having the same word in both places, you call special attention to it: Water alone dug this giant canyon; yes, just plain water.
Many writers use epanalepsis in a kind of "yes, but" construction to cite common ground or admit a truth and then to show how that truth relates to a more important context: Our eyes saw it, but we could not believe our eyes.