"What the soul is to the body, Christians are in the world." So the Epistle to Diognetus in the late second century. Reformulated for modern community, it has been altered to say: "What the soul is to the body, the church is to society [or the nation]."
But such a conception of the church is disastrous on any number of accounts. Schooled by Paul and by Jesus, we would be better to say: "The church is not a soul within the body of society or the nation, much less the soul of any one society or nation. Rather, the church is one particular and irreducible body politic within another."