What is the real Church, the true mother of all Christians? According to St. Paul, she is, first of all, "the Jerusalem above." Therefore, she is not of this world. She is not an earthly, bodily, visible kingdom, but an invisible, spiritual, heavenly one. She is not an institution perceptible to the senses, not a number of people who are bound by certain laws and customs. Instead, she is a kingdom of hearts that are bound together in one understanding and one Spirit. What holds her together is unseen by the eyes of people. She is not a host of people who can be recognized by natural descent or by the country in which they reside. She is bound to no nation or city of the world. She is a congregation that is dispersed over the face of the entire earth, and she has members of every age and station among all people everywhere.
Furthermore, the apostle says, the Church is "free." There are no children of Hagar, no Ishmaels, none who by their human birth alone belong to her as servants of the Law. She is made up entirely of Sarah's children, of Isaac's, of pure children of the promise, namely those who are born again by the promise of grace as free children of God.
The true Church is thus the whole number of those who have sought and found their salvation, not on Sinai, but on Golgotha. -- C.F.W. Walther, *God Grant It* - Tuesday of Lent IV (sermon on Gal. 4:26)