Here's a video of him speaking at the Transforming Theology session at the American Academy of Religion:
When I hear both my progressive friends and my evangelical friends talk about atonement, it's usually an either/or argument. Either the cross is only about the forgiveness of sins, or it's only a means of liberation for the marginalized. However, from what I understand of the Bible, it's not an either/or question: it's both/and. The Gospel is about both justice and justification.
First, there's justification. When the Pharisees asked why Jesus would share His meals with sinners, He replied, "It is not the healthy who need a doctor, but the sick. I have not come to call the righteous, but sinners" (Mark 2:17). Later on during the Last Supper, He tells His disciples that the bread and wine represent His body and blood, which are broken and shed "for many for the forgiveness of sins" (Matthew 26:27-28). Jesus, according to 1 John 2:2, is the "atoning sacrifice for our sins, and not only for ours but also for the sins of the whole world."
Without the Cross, we have no hope for forgiveness. We're stuck with our sin, our guilt, and our shame. It's only through the Cross that we are free from our sins.
Ah, but what about justice? Well, throughout the Old Testament the prophets call for justice among the nations. For example, there's this prophecy Isaiah has for "the rulers of Sodom" and "the people of Gomorrah:"
"'The multitude of your sacrifices— what are they to me?' says the LORD. 'I have more than enough of burnt offerings, of rams and the fat of fattened animals; I have no pleasure in the blood of bulls and lambs and goats. When you come to appear before me, who has asked this of you, this trampling of my courts? [. . .}
Wash and make yourselves clean. Take your evil deeds out of my sight; stop doing wrong. Learn to do right; seek justice. Defend the oppressed. Take up the cause of the fatherless; plead the case of the widow.'" (1:11-12, 16-17)
Then later on chapter 10 beings with this lament:
"Woe to those who make unjust laws, to those who issue oppressive decrees, to deprive the poor of their rights and withhold justice from the oppressed of my people, making widows their prey and robbing the fatherless. What will you do on the day of reckoning, when disaster comes from afar?
To whom will you run for help? Where will you leave your riches?" (verses 1-3)
In fact, now that I think about it, this reminds me a lot like what Jesus says to the Pharisees:
"Woe to you, teachers of the law and Pharisees, you hypocrites! You give a tenth of your spices—mint, dill and cumin. But you have neglected the more important matters of the law—justice, mercy and faithfulness. You should have practiced the latter, without neglecting the former." (Matthew 23:23)
If Jesus loves the spiritually marginalized, then I'm pretty sure He wants us to love the socially marginalized, too.
Now I'm only an amateur theologian at best, but if I'm reading these verses correctly it seems like justice and justification are two sides of the same coin. You cannot have one without the other, or else it's not really the Good News.