Commentators explain that God is speaking directly to the grief of Israel, personified by Rachel weeping for her exiled children. The promise is that their sorrow and suffering ('thy work') will not be in vain. God will bring a 'reward' by graciously restoring His people from 'the land of the enemy'—a direct reference to their return from captivity in Assyria and Babylon. This is a powerful assurance that national despair is not the final word.