If you're ready to really dive into theology, The Proper Distinction Between Law and Gospel by CFW Walther is the go-to text among many Lutheran denominations. It's a collection of his lectures from his time as a professor at Concordia Seminary.
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The Proper Distinction Betw...
Augsburg and Constantinople: The Correspondence between the Tubingen Theologians and Patriarch Jeremiah II of Constantinople on the Augsburg Confession