When I became a police officer one of my objectives was advocating justice for people. It's a popular social concept; after all, nobody supports injustice. I now realize that although most people praise justice, many have not attained it. Justice still remains a "hope".
Fundamentally the rich are unjust to the poor, the powerful are unjust to the weak, the poor and the weak are unjust to each other.
The most important element to remember about justice is that it is all about rights and obligations, e.g., if a person has a right, others have a duty to honor it. If I have a right to life you have an obligation not to kill me; if you have a right to your property I have an obligation not to steal it; if hungry children have a right to food we have an obligation to see that they get it.
In one way or another we are all obligated to the rights of others because we share our humanity. Over time society, through government, religious institutions and the courts, has arranged things so that individuals and groups respect each others' rights. In so doing, justice can be measured and judged.
In my desire to advocate for justice I found that it would be lacking if we are not just in our own hearts.