This episode introduces chapter 8 so that everyone understands the importance of the event that's about to take place: namely that here Moses instituted the use of anointing by title. And that the Greek rendering of the title for High Priest is "Christ." In Hebrew it's "HaMesshiah" and in modern English that is, "Messiah." So Aaron was anointed as Christ, which is why Jesus said the book (Septuagint in His time) testifies of Him (it literally mentioned Him by name hidden in the titles for king and High Priest). There's more in the episode.