The death and the life of the Christian is not determined by his own resources; rather he finds both only in the Word that comes to him from the outside, in God’s Word to him. The Reformers expressed it this way: Our righteousness is an ‘alien righteousness’ a righteousness that comes from outside of us (extra nos). They were saying that the Christian is dependent on the Word of God spoken to him. He is pointed outward, to the Word that comes to him. The Christian lives wholly by the truth of God’s Word in Jesus Christ. If somebody asks him, Where is your salvation, your righteousness? he can never point to himself. He points to the Word of God in Jesus Christ, which assures him salvation and righteousness. He is as alert as possible to this Word. Because he daily hungers and thirsts for righteousness, he daily desires the redeeming Word. And it can come only from the outside. In himself he is destitute and dead. Help must come from the outside, and it has come and comes daily anew in the Word of Jesus Christ, bringing redemption, righteousness, innocence, and blessedness.
But God has put this Word into the mouth of men in order that it may be communicated to other men. When one person is struck by the Word, he speaks it to others. God has willed that we should seek him and find his living Word in the witness of a brother, in the mouth of a man. Therefore, a Christian needs another Christian who speaks God’s Word to him. He needs him again and again when he becomes uncertain and discouraged, for by himself he cannot help himself without belying the truth. He needs his brother man as a bearer and proclaimer of the divine word of salvation. He needs his brother solely because of Jesus Christ. The Christ in his own heart is weaker than the Christ in the word of his brother; his own heart is uncertain, his brother’s is sure.
And that also clarifies the goal of all Christian community: they meet one another as bringers of the message of salvation. As such, God permits them to meet together and gives them community. Their fellowship is founded solely upon Jesus Christ and this ‘alien righteousness’. All we can say, therefore, is: the community of Christians springs solely from the biblical and Reformation message of the justification of man through grace alone; this alone is the basis of the longing of Christians for one another.
From the chapter called ‘Community’ by Dietrich Bonhoeffer in Life Together, 1949.