I learned in Laoshan that someone at the foot of the mountain brought rice, regardless of the willy-nilly, grab a bowl and eat it. What is the function of this plan here?

It shows that the Red Army soldiers are eager to race against time and hope to defeat the ambition of old Shan Ye at an early date.

Their hunger is in sharp contrast to the fact that they finally overcame the old mountain boundary, which shows that they still rely on tenacious perseverance and fearless spirit even in hunger.