What is symbolic of the Danaids...?

In the story of the Danaids, as punishment for murdering their husbands, the 49 of them that had committed the crime were sentenced to carry water in jugs for the rest of eternity. The jugs were filled with holes causing them to have to constantly go back and forth between the river to refill the jugs. What is symbolic of this? How was this supposed to "teach a lesson"?