Either Christ must live and the Law perish, or the Law remains and Christ must perish; Christ and the Law cannot dwell side by side in the conscience. It is either grace or law. To muddle the two is to eliminate the Gospel of Christ entirely.
 Martin Luther, Commentary on the Epistle to the Galatians (1535). copy citation

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Author Martin Luther
Source Commentary on the Epistle to the Galatians
Topic conscience Christ
Date 1535
Language English
Reference
Note Translated by Theodore Graebner
Weblink http://www.gutenberg.org/files/1549/1549-h/1549-h.htm

Context

“To paraphrase this sentence: "These false apostles do not merely trouble you, they abolish Christ's Gospel. They act as if they were the only true Gospel-preachers. For all that they muddle Law and Gospel. As a result they pervert the Gospel. Either Christ must live and the Law perish, or the Law remains and Christ must perish; Christ and the Law cannot dwell side by side in the conscience. It is either grace or law. To muddle the two is to eliminate the Gospel of Christ entirely. It seems a small matter to mingle the Law and Gospel, faith and works, but it creates more mischief than man's brain can conceive. To mix Law and Gospel not only clouds the knowledge of grace, it cuts out Christ altogether.
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