“A bigger question is why a rav needs to shlep out Seuda Shlishis when people are waiting to daven Maariv.”
There is a famous story that the Chofetz Chaim, may his merit protect us, shlepped out shalosh seudos when people were waiting to daven Maariv. The reason for this is well-known, that the souls of the wicked do not return to Purgatory until after Shabbos is over. Shabbos is over at the time that WE (in this world) make it be over.
The longer a person kept Shabbos in this world, the longer he will get to stay out of Purgatory in the next world.