From the final pages of Here We Stand (pgs. 186-188):
"It is the plain teaching of the New Testament that the true unity of the church is unity in the truth. And it is the painful experience of church history, particularly during the last century, that whenever attempts have been made to unite churches without inquiring about pure doctrines-that is, without establishing what truth is, and what error, in Christianity-unity has not been achieved; and, what is worse, the divisions have always been magnified.
"There is unity in the church when it has one Lord, the Christ who is really present in His Word and Sacrament. This unity can become manifest in the historical church, however, only when we agree in our profession of faith in this one Lord and in the one truth of the Gospel. The unity of the historical church is not achieved though conformity in rites and ceremonies, nor though identical orginization and life-patterns, nor even throiugh uniformity in theological thought-forms and opinions. Such unity is only achieved when, in the joyful assurance of our faith in our Lord Jesus Christ, we are one in our understanding of what His saving Gospel is and one our understanding of what He gives us in His Sacraments. 'For the true unity of the church, it is enough,' the Augsburg Confession states. It is, indeed, enough. But it is also necessary...
"[The Lutheran Church] knows, too, that we cannot bring about unity by ceasing to take the search for truth seriously. For the prayer, 'that they may all be one,' is inseparably connected with the other petition, 'Sanctify them in the truth; Thy Word is truth.' So we pray with the Fathers of the Reformation, in the same hymn, 'Lord, keep us steadfast in Thy Word,' and 'Send peace and unity on earth.' The Lutheran Church has been bearing up under the reproaches of the world for the past four hundred years because it believes that it is the Lord who passes judgment, and that the existence of the church depends on His judgment alone."