Traditional Protestant accounts of Paul's theology are often criticized for their inability to relate justification by faith and the participatory categories of Paul's thought. The two are driven apart by sharp distinctions between declaring and making righteous, between justification as a once for all external act and regeneration as an internal lifelong process. The way is left open for justification to be treated as a legal fiction. Contrary to popular misconceptions, these difficulties do not stem from Martin Luther. In his exegesis of Paul, Luther intimately connects justification by faith and participation in Christ, integrating the two effectively. This article explores the manner in which Luther does so, evaluating his exegetical conclusions and assessing their relevance for contemporary attempts to interpret Paul's theology.