"The Scriptures speak of the church quite simply and use the term in only one sense...according to the Scriptures, the church is called the assembly of all believers in Christ on earth.... This community or assembly consists of those who live in true faith, hope, and love. As Paul says in Ephesians 4:5, 'One baptism, one faith, one Lord,' though they be a thousand miles apart in one body. Yet they are called an assembly in spirit because each one preaches, believes, hopes, loves and lives, like each other.... This really means a spiritual unity, and because of it men are called a communion of saints. This unity of itself is of itself sufficient to make a church, and without it no unity, be it of place, of time, of person, of work, or of whatever else, makes a church." Martin Luther, Select Writings of, Vol. 1, 207
Reformers refer to this, as the "invisible church" of Jesus Christ, Who is its' Head and High Priest.