A little leaven . . .

The individual must realize that his hours of aloneness react upon the community. In his solitude he can sunder and besmirch the fellowship, or he can strengthen and hallow it. Every act of self-control of the Christian is also a service to the fellowship. On the other hand, there is no sin in thought, word, or deed, no matter how personal or secret, that does not inflict injury upon the whole fellowship. An element of sickness gets into the body; perhaps nobody knows where it comes from or in what member it has lodged, but the body is infected. This is the proper metaphor for the Christian community. We are members of a body, not only when we choose to be, but in our whole existence. Every member serves the whole body, either to its health or to its destruction. This is no mere theory; it is a spiritual reality.

Dietrich Bonhoeffer, Life Together (p. 89)