Marcus summoned the trio of near-death experiences at the guild for their first-ever guild mission. Guild missions were important since the ID card that they get marks what rank he guild decides they are, not the Circle of Pillars, so if someone was A-rank, but never completed a guild mission, they would still be considered F-rank and given that salary, instead of what an actually A-rank would make.
Guild missions were generally simple at the start, so from F-rank to C-rank, almost, the missions wouldn't necessarily be about testing your prowess; they would mainly be about helping out the community in any way possible. But if you are C-rank, maybe helping out the community may require, in certain situations, some violence, like stopping robbers, or armed people, and stuff along those lines.