A sieve would separate large particles from smaller ones. It was used in agriculture to separate any rocks or other particles from the grain. In this case, it seems as if the pebble represents sinful leaders, none of whom would escape the sieve of God’s judgment.1
9 “For behold, I will command, and shake the house of Israel among all the nations as one shakes with a sieve, but no pebble shall fall to the earth.