he - the enemy; or rather, God (Psa 2:9; Jer 19:11).
It - the Jewish state.
potter’s vessel - earthen and fragile.
sherd - a fragment of the vessel large enough to take up a live coal, etc.
pit - cistern or pool. The swell of the wall is at first imperceptible and gradual, but at last it comes to the crisis; so the decay of the Jewish state.