For reformers such as Martin Bucer (1491-1551), a true response to the Word of God involved incorporation into the church, the body of Christ on earth. Soteriology and ecclesiology were inseparable, and the Christian life could not be undertaken without becoming part of into the community of believers. Integration in the body evidenced true faith, as the believer eschewed individualism and personal autonomy and embraced the preaching of the Gospel, submitted to the discipline of the assembly, and sought to edify the church.

Believers Must Be Integrated into the Body of Christ

It is essential for all the elect to be integrated with one another by the deepest knowledge of their faith and by true love, since otherwise they will not cohere in the body of Christ.This efficacy of the Word of God must be stressed first of all. Therefore it is not enough for the gospel to be preached or to hear it, but once it has been heard the hearer must be taught, must profess faith and must be subjected to the discipline by which pastors, together with their elders, ensure that everyone in the church maintains its order in all things. Therefore this efficacy of the Word of God must be stressed first of all. By it we are integrated into one body, whose head is Christ, so that we may be led to him and not allow ourselves to be drawn away from him. It is also to be noted what Paul says, that the many gifts have been given for the work of the ministry, that is, for the edification of that body that is the church.

Lectures on Ephesians 4:7-16.

Gerald L. Bray, ed. Galatians, Ephesians. Reformation Commentary on Scripture, NT Vol. X, p. 349.