Zacharias Ursinus (1534–1583) was a German Reformed theologian and the leading teacher of the Reformed churches in the Palatinate. Trained at Wittenberg and Geneva, he became professor at Heidelberg and head of its College of Wisdom. He is remembered chiefly as the principal author of the Heidelberg Catechism of 1563, whose teaching he expounded in the lectures published as his Commentary on the Heidelberg Catechism.
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A short treatise by Zacharias Ursinus, the theologian behind the Heidelberg Catechism, published in 1583, answering the question: what is the gospel? Ursinus sets out the good news of God's promise in Christ and distinguishes it from the law. A brief, clear specimen of early Reformed teaching for ordinary readers.