From the Augsburg Confession (1530), Article VII:

We teach that one holy Church is to continue forever. The Church is the congregation of saints, in which the Gospel is rightly taught and the Sacraments are rightly administered.

As to the true unity of the Church it is enough to agree concerning the doctrine of the Gospel and the administration of the Sacraments. Nor is it necessary that human traditions, that is, rites or ceremonies, instituted by men, should be everywhere alike. As Paul says: One faith, one Baptism, one God and Father of all, etc. (Eph 4:5-6).