The auditorium was a large, semi-circle shaped building with hordes of chairs. On this specific day, many (too many) of these chairs were empty. Naturally, the audience was scattered around the building, sitting in different chairs all over the place.
Audience members don't really care where they sit (as long as its not right at the front), but, as you'll read below, for a speaker a scattered audience can be both demoralizing and energy-draining.
Judgment Starts at the Back
So before commencing his speech, the speaker asked the audience to move forward. He didn't give a stern command, but made light of the situation by promptly informing everyone that "Judgment starts at the back".
Are there disadvantages when speaking to a scattered crowd?
Audience size isnt as important as audience density. Any speaker who's had to present in huge half-empty halls will tell you that its frustrating and tiring.
The vast amounts of empty space turns into an insatiable gaping hole that sucks all the energy right out of the room, and will have you, the speaker, struggling to maintain your energy and keep your efforts regulated, since it feels like your speaking into nothingness.
So how do you get people to move forward?
Ask them. They'll likely appreciate your honesty about the less-than-desirable state of the room and will oblige. I've written elsewhere about the high value audiences place on honesty and authenticity - so don't pretend like you don't notice the room looks and feels like a deserted cave. You can admit to the audience that the dead space will kill you long before they fall asleep, so could they please move forward a bit...
I once attended a weekend conference in England which, though heavily promoted, grew an only modest crowd on the Saturday, which was the main day for the event. The icy London weather had probably more to do with the audience size than the main presenter, who was a seasoned speaker with an entertaining style.
If you're smart you may, like the speaker in my story above, make light of the situation by turning it into a game, being humorous about it or, if your audience is young and tie-less, giving out free gifts to people taking up front-row space.
Some people likely won't budge and that's fine. Not everyone wants to shift seats so just leave the laziest of the bunch in the back. Most people however won't have a huge problem moving towards the front of the auditorium when requested to do so by a speaker.