According to my 'red letter' (King James) Bible, Jesus talked as much about justice as he did about loving one another--more, if you leave out the Book of John (so, the synoptic Gospels). The concern of justice--for Jesus and secular philosophers--is people's actions involving one another. Didn't Jesus make it clear that our relation with God is reflected in our relations with other people--first and foremost, our actions involving them, how just (or unjust) we are? A strictly rational ethic of justice, involving no belief of any kind, is not less just for being rational--and surely not less so for people who believe God created us, with our capacity for rationality. (Linked article is here in Medium, but not behind the paywall.)