Packer: Sola Gratia understood in varying degrees of adequacy

"The doctrine of free justification by faith only, which became the storm-centre of so much controversy during the Reformation Period, is often regarded as the heart of the Reformers' theology, but this is hardly accurate. The truth is that their thinking was really centered upon the contention of Paul, echoed with varying degrees of adequacy by Augustine, and Gottschalk, and Bradwardine, and Wycliffe, that the sinner's entire salvation is by free and sovereign grace only. The doctrine of justification by faith was important to them because it safeguarded the principle of sovereign grace."

- J.I. Packer & O.R. Johnston
Historical and Theological Introduction
in Martin Luther's The Bondage of the Will
(Fleming H. Revell, 1957) p.58 (Ed. Scott Larsen)