This is good news. I hope that it will translate into some effective action.
Edit: Misleading headline. This is an advisory opinion, which appears to be non-binding. I don't think "ruling" is entirely appropriate.
In general, advisory opinions are not binding, but may inform the development of international law. According to the ICJ website, advisory opinions:
"carry great legal weight and moral authority. They are often an instrument of preventive diplomacy and have peace-keeping virtues. Advisory opinions also, in their way, contribute to the elucidation and development of international law and thereby to the strengthening of peaceful relations between States."