The ICJ is powerless. How does it purpose to enforce it, or anything?
The ICJ can issue warrants for individuals, and the many signatories are then obliged to arrest those people should they travel. Even Kissinger had to take care where he changed planes.
The International Court of Justice (ICJ) settles legal disputes between UN member States, and it's rulings are expected to be upheld and enforced by UN States, or ultimately the UN Security Council.
The International Criminal Court is the one that can issue arrest warrants against individuals.