To this point in the discourse, the Savior has reiterated the promise to gather Israel, but has also reiterated that it is an even that lies in the future. At this point he begins to answer the question of when that might be. He tells them that he will give them a sign.
Textual: This is a continuation of the discourse given in chapter 20, and should be read as a continuation of that topic. The chapter break was not part of the 1830 text.