Luther called justification by faith alone (i.e. apart from works) the doctrine by which the church stands or falls.

"From," this book "which clearly enunciated Luther's great theme of justification by faith, it can be certain that Knox was squarely in the mainstream of the Reformation's purpose of restoring the gospel of Jesus Christ to its rightful place... The Scottish reformer asserted that the wicked believe works to be a part of salvation, but a true preacher must exclude them from justification as did Christ and the prophets.  Yet Knox did not condemn good works, for as shall be seen, he held them to be a fruit of justification, but not the cause of it.... Finally, he contended that the faith of the Old Testament fathers and that of the New Testament, which he possessed, were one and the same. The patriarchs stood in God's favor in the future promised Seed, and Knox stood in God's grace by faith in the Seed that had already been revealed. Such a position of exact continuity in the promise of the gospel and in the content and object of the faith bore some resemblance to the 'Federal Theology' or the covenant theological system that developed more formally at a later date" (Kyle, The Mind of John Knox, pp. 85, 98).