“In many ways, however, the reformers’ views on the church represent their Achilles’ heel. The reformers were confronted with two consistent rival views of the church the logic of which they could not match – those of their opponents within the Catholic and Radical Reformations.”
…
“The Reformation can, at least in some respects, be seen as a replay of the Donatist controversy of the fourth century. Luther, it seemed, could only uphold Augustine’s doctrine of grace by rejecting Augustine’s doctrine of the church. ‘The Reformation, inwardly considered, was just the ultimate triumph of Augustine’s doctrine of grace over Augustine’s doctrine of the church.’ (Benjamin B. Warfield).”
McGrath, Historical Theology, pg. 200