Justice is always couched in the language of measuring something against a perfect standard. If the thing falls short of what is right and good, we call it unjust; if it upholds what is right and good, we call it just.
But unless a theistic framework is used (and, I believe, specifically a Judeo-Christian one), no individual can level accusations of what is right or wrong, what is good or bad, and of what we ought or ought not do.
The two options then become:
- Approach justice from within a theistic framework: This means the anti-theist has not only ceded the high ground, but all ground upon which to stand.
- Reject the theistic framework: This makes the anti-theist unable to offer any guidance as to what justice could possibly mean, because temporary justice is simply no justice at all — it will either be utilitarian (“Let’s do this because it seems to work and make people happy.”) or humanistic (“We humans make our own rules so we should try to be nicer, I guess.”) or fatalistic (“This is the best we’ve got; we’ve never done better as a species and we probably never will.”).
When Marcus Aurelius wrote that injustice is impiety, I believe he was being perfectly rational and I think he was right. Injustice is an affront to a perfect being. But be certain of this: that thought came from the seedbed of theism. It could not have come from anywhere else and it cannot find its ultimate expression apart from an eternality imbued with perfect justice.