To think that how a society deals with the questions of right and wrong, good and evil, and the improvement of society along those lines, is /not/ within the normal working of the Church is a strange idea.
Christianity makes claims about both knowledge and action in the world that are radically different from other interpretations of the world, most of which broadly agree with one another. It is a reproach of all competing accounts of both knowledge (knowledge in general, but certainly moral knowledge, and therefore the basis upon which right action is undertaken), and action.
Therefore, Christianity wherever it goes is a reproach to authority and demands a reordering of individual souls and of society as a whole in accord with a right view of what humans are, what the universe is, who God is, and so what our duties are to humans, the universe and God.
Because of this antithesis, Christian Activism is built into the fabric of the Christian life. There is nowhere the Gospel goes where the Kingdom of Jesus Christ is not proclaimed, and this is no empty claim of dominion, but the kind that has the authority that lets Paul announce to the authorities on Mars Hill, “The times of ignorance God overlooked, but now he commands all people everywhere to repent…” (Acts 17:30, ESV)
Note the claim of authority is epistemic (knowledge) as well as a call to right action, and that the claim is universal, directed toward “all people everywhere.”
No exception is given for rulers, lawmakers, police, judges, or any other institution. Christ’s authority does not currently coincide with His dominion as it will on the Last Day, but every Christian is a herald of that dominion, and the command is present tense, not eschatological.
This is why every Christian has some responsibility for activism toward the improvement of society in accord with the standards of the word of God; “You shall love your neighbor as yourself.”