The social and political witness of the church is simply being the church.That's it. The church should be the church. That's Christian political engagement, being the church. Or, at the very least, having political activism flowing out of the life of the local church.
This imperative distinguishes the church from conservative and liberal/progressive Christian politics, which can be tempted by theocratic impulses and, thus, contaminated by Constantinianism and the temptations of Empire.
Being the church--really being the the church--is a political intervention, the church is a counter-politics to the politics of the State. Which means that to think politically in the church is to think locally, focusing on addressing our social and moral ills within the common life of the local congregation.
For example, the goal of the local church is to "have no needy person among you" (Acts 4.34). We are to address poverty locally in our communal sphere of influence, among ourselves. To have no needy person among us.
Relatedly, we also deal with issues of work locally. Paul says that "the one who doesn't work shall not eat" (2 Thess. 3.10). Importantly, that statement has nothing to do with the welfare state and entitlements. Paul is speaking to a local, congregational, and relational issue. The conversation about work is between people who know and love each other.
For example, at Freedom Fellowship we serve a weekly meal. And sometimes you hand a mop to someone and say, "Hey man, it's your turn to clean up."
The point here is that the Christian approach to poverty and work is inherently personal, relational and local. Christians practice a "small politics." These aren't laws being passed by the government but a common life being negotiated among friends.
The State is no substitute for the church. The call, then, isn't to give up the church for political activism but to invest more radically in becoming the church.
I'm put in mind of a quote by G.K. Chesterton that I'd like to tweak:
"The church has not been tried and found wanting; it has been found difficult and not tried."--from an unpublished post contrasting the small, relational politics of the church with the political engagement found among evangelical and progressive Christians