For most TV shows, the opening titles feature a montage of things that tie in with the series, or just interesting visuals and a catchy tune, but some opening themes reveal hidden details to come for the series. An opening theme is a good way to set the tone for a show with the theme song reflecting the mood of the series, and the major credits for the series displayed. Some shows use this to great effect, establishing the premise of the series, as seen in shows like The Fresh Prince of Bel-Air.

https://screenrant.com/tv-opening-themes-contain-plot-points/