The phrase "social justice" has become, like so many other things, a tribal marker in the culture wars. To call for "social justice" is to code yourself as left-wing. To decry "social justice" is to code right-wing. And this is why, as a Christian, I struggle so much with our current political discourse.
Here's what liberation theology gets right: God really does have a preferential option for the poor and the oppressed. I don't know how any Biblically literate person can avoid that conclusion. Psalm 72 is a great example of this:
For he will rescue the poor who cry out
and the afflicted who have no helper.
He will have pity on the poor and helpless
and save the lives of the poor.
He will redeem them from oppression and violence,
for their lives are precious in his sight.
That said, this vision of peace and justice is placed in the hands of the Davidic king. And as the Biblical story unfolds, the Davidic monarchy fails to realize these ideals. The prophets begin to look forward toward a Messianic king who will usher in God's good and righteous rule. Psalms like Psalm 72 become songs of messianic hope.
At this point, when it comes to the kingdom proclaimed by Jesus, interpretations start to divide. Does Jesus spiritualize and eschatologize these visions of social justice? Or does Jesus call us to seek social justice, as in the Hebrew imagination, in the here and now?
I think it's both. If Jesus rules the cosmos from God's right hand as the Anointed One, then the affairs of earth should be brought into conformity with his rule. As Jesus prayed, may the kingdom come on earth as it is in heaven.
And yet, the full and final establishment of God's just rule can only be realized by God's decisive intervention in history. Until then, we are left with a broken politics and broken political leaders. So we seek social justice, but know that we shall only ever secure a tenuous and poor approximation of the kingdom of God. Christian political engagement, therefore, is a mixture of both lament and hope.
Now, as to the shape and content of Christian political engagement, I think Psalm 72 is a great place to start. Call it social justice or call it whatever, but let us "rescue the poor who cry out and the afflicted who have no helper."