When the mainsail isn't used, it's "brailed up" and stowed in a bundle along the main mast and the headrope running to the sprit, which is what's going on here.
I'm operating the brail winch which takes the main weight, while David L and Roger haul on the Lowers and Middles to gather the lower part of the mainsail to the mast. Two other people will be on the Uppers and Peaks, which gather the upper part of the sail to the headrope.