1)
Why does it mention saving the Oni?
1.
Radak: This is why all nations will love him and serve him, for they will see that he is a virtuous king, and saves the poor who have no helpers; he helps them!
2.
Malbim: He himself will save the poor, who have no helpers, from their oppressors, and not via the judges that he appointed in every city. Via this he will merit to rule from sea to sea.
