Martin Bucer was John Calvin's "father in the faith."
The ff. is sourced from Brian Lugioyo's Martin Bucer's Doctrine of Justification: Reformation Theology and Early Modern Irenicism (Oxford Studies in Historical Theology):
By faith alone means that in faith Christians contemplate Christ, and because faith comes with the bestowal of the Spirit of Christ, they become possessed by him so that believers now live in him and he in them. In this sense of mutual inhabitation, Christians are allowed to cooperate with God in salvation, since these works are not their own but the work of Christ in them. This agency is expressed in Bucer primarily in terms of the bestowal of the Holy Spirit, [285] being clothed in Christ, [286] participation in Christ, [287] being in communion with Christ, and so forth. [288] If a believer “does any good, it results from the fact that he is a creation of God, created for good works, works which God himself prepares, makes and performs, so that he rewards in us gifts which are already his.” [289] Hence, Bucer follows Augustine’s view that “when God crowns our merits, he crowns nothing but his own gifts.” [290] Merit is not the result of works but the result of the believer cooperating with the Spirit who works within the believer:
Nevertheless, when God wants us to cooperate with him by good works for our salvation, or rather, even to “work it out” (κατεργάζεσθαι) [Phil. 2:10] and has thus determined to repay us according to our deeds, there is brought about also in its own way our justification; that is, eternal life is assigned to us as a result of works. But this is the case only when through our election and the purpose of God formed before the ages, there is already assigned to us before the foundation of the world this life of God as a result of the grace of God and the merit of Christ [Ephesians 1 and 3]. This life moreover is assigned to us through faith, that is, after we believe in Christ and have in some way become already possessed of him. This of course comes about at that blessed beginning of faith which belongs to the sons of God through the Spirit, who is the pledge of this inheritance. For good works are the fruit of this faith and of the Spirit. [291]
Works are in a sense a cooperating cause, which Bucer speaks about as a secondary cause elsewhere.
