Justice is active, and justice is something we have to roll up our sleeves and be involved in. Whatever humility works out to be, it's not a destination. It's a journey. One Bible commentator I read said that the three requirements correspond to the messages of three of the prophets in the Old Testament. Justice was the message of the prophet Amos.
Mercy is the theme of the prophet Hosea.
I desire steadfast love, and not sacrifice, the knowledge of God, rather than burnt offerings. . . Walking humbly, this person suggested, is part of the message of the prophet Isaiah. There's that theme of justice again. So, maybe our verse from Micah is a summary of the teaching of the prophets. Another way to look at these three requirements, if you want to use a Trinitarian image, is that justice is what God the Creator requires.