Why should we be concerned with justice for other people?

Are you willing to put up with being treated unjustly? Does it make you angry when life doesn't seem fair and others seem to receive preferential treatment?

If you love your neighbour as yourself, then you will feel angry when your neighbour is treated unjustly, too, won't you?

The propeht Micah was very clear on how highly God values justice,

"What does the Lord require of you? To act justly and to love mercy and to walk humbly with your God" (Micah 6:8)