Faith supporting justice?

I am a Christian, and I care very much about social justice. I like to think that my faith inspires and fortifies my justice work. I like to think that faith makes justice work richer and more powerful than it would be without an understanding that God is permeating everything.

But I look at the world and don't see that faith makes a difference. I know people who are passionately committed to justice -- but either don't believe in God at all, or maybe believe that in some vague and undefined way God is behind it all, but God is never at the forefront of their attention.

I would like to be able to invite them into faith. I would like to say that faith commitment does not detract from their justice commitment but instead makes it all the more real and powerful. But I don't see how that's true. I don't see that they're missing anything. If anything, they seem to be able to be much more sane and balanced than I am. They can work hard, do what they can, and let the rest be. If I'm doing all things as if I'm working for God, how can I ever say that I've done enough and now it's time to go play? But of course that way of life is unsustainable.

All this seems decidedly backwards.