Despite being charged with innovation, the Protestant Reformers insisted that they sought not to invent any new doctrine but rather to recover the faith entrusted to the church and confessed since ancient times. Proof of this can be seen in their ecclesiology—their doctrine of the church. The Reformation church did not cast aside the ancient church’s understanding of itself but rather maintained it. Proof of this is evident in that the Reformers adopted the classic ecumenical creeds, including the Apostles’ Creed. This creed confesses belief in “one holy catholic and apostolic church,” giving us four truths about the church of Christ: its unity, its holiness, its catholicity, and its Apostolicity.
Today we will consider church unity. Simply put, there is only one church of Christ. Despite the institutional and denominational diversity of the visible church, the true church of Jesus Christ consists of one body. Paul teaches us this truth in today’s passage (Eph. 4:4–6).
In Paul’s day, there were many individual, distinguishable churches, each with its own leadership and membership. The church in Corinth was not precisely identical to the church in Ephesus, which was not identical to the church in Philippi or in Antioch. Thus, when Paul makes reference to the oneness of the church, he must be referring to something that transcends local manifestations of the visible church. He is referring primarily to the one invisible church, the universal church that is made up of everyone who is united to Christ by faith. Local churches may vary in their visible expression, but the church is finally and invisibly one. It is united in faith (v. 5), that is, the truth. Doctrinal differences are real and should not be ignored, but there is a core faith defined by the gospel that unites all Christians regardless of where they hold their local church membership.
John Calvin comments on today’s passage: “Christ cannot be divided. Faith cannot be rent. There are not various baptisms, but one which is common to all. God cannot cease to be one, and unchangeable. It cannot but be our duty to cherish holy unity, which is bound by so many ties. Faith, and baptism, and God the Father, and Christ, ought to unite us, so as almost to become one man.” Differences between believers remain, but because of the oneness of the true church, we cannot fail to recognize as Christians those who profess the biblical gospel, for when we do so we deny the reality of the one, invisible church that transcends our local assemblies.