Jon Snow has been wanting to take care of the mutineers at Craster's Keep for some time, but Alliser Thorne hasn't consented because they can't spare the men. However, when Janos Slynt makes the point that it would be a good opportunity to rid themselves of him for good, he changes his mind. Jon happily accepts, and his first task is to ask for volunteers to aid him in his mission. At first it seems like a lost cause, but eventually enough people volunteer to make Alliser and Janos think twice about what they've done. This scene is another small step towards establishing Jon as a leader. He is popular among the brothers, so much so that he is a genuine threat to Alliser Thorne's position of power. When it comes time to vote for a Lord Commander, Jon has a good shot at being voted into that position, as evidenced by the amount of people who willingly choose to go with him beyond the Wall. Janos and Alliser were not expecting this, which makes it so satisfying to see their faces as their plan backfires. Not only does Jon now have a better chance of coming back alive, but now they have definitive proof that Jon is the threat they feared. It's not a big scene by any means, but it does a good job setting up for events to come.
