Wiktionary
the thing is
phr. (context idiomatic colloquial English) (non-gloss definition: Used to introduce the main point or issue)
Usage examples of "the thing is".
All we have to do to open the thing is to advance the clock so it thinks it is the morning.
Some other arrangement will have to be arrived at, if the thing is ever to be taken to the Antiquarian Museum.
A meeting in the street, an introduction, an invitation-- the thing is done.