“Why was Luther not satisfied  with lecturing and preaching?  Why did he take up the pen?  The primary reason was not the urge of the scholar nor the controversial zeal of a reformer, but the responsibility of a pastor for a pure, clear, comprehensible, convincing and liberating proclamation of the gospel.  He had himself struggled to understand the righteousness of God, which, as the gospel reveals, means that the righteous live by faith.  This struggle had to be proclaimed publicly to the language in which they spoke….”

(Luther:  An Introduction to his Thought)

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