“The charge that Luther adapted the translation to his theological opinions has become traditional in the Roman Church, and is repeated again and again by her controversialists and historians.
In both cases, the charge has some foundation, but no more than the counter-charge which may be brought against Roman Catholic Versions.
The most important example of dogmatic influence in Luther's version is the famous interpolation of the word alone in Rom. 3:28 (allein durch den Glauben), by which he intended to emphasize his solifidian doctrine of justification, on the plea that the German idiom required the insertion for the sake of clearness. But he thereby brought Paul into direct verbal conflict with James, who says (James 2:24), "by works a man is justified, and not only by faith" ("nicht durch den Glauben allein"). It is well known that Luther deemed it impossible to harmonize the two apostles in this article, and characterized the Epistle of James as an "epistle of straw," because it had no evangelical character ("keine evangelische Art").
He therefore insisted on this insertion in spite of all outcry against it. His defense is very characteristic. "If your papist," he says,
The Protestant and anti-Romish character of Luther's New Testament is undeniable in his prefaces, his discrimination between chief books and less important books, his change of the traditional order, and his unfavorable judgments on James, Hebrews, and Revelation. It is still more apparent in his marginal notes, especially on the Pauline Epistles, where he emphasizes throughout the difference between the law and the gospel, and the doctrine of justification by faith alone; and on the Apocalypse, where he finds the papacy in the beast from the abyss (Rev. 13), and in the Babylonian harlot (Rev. 17). The anti-papal explanation of the Apocalypse became for a long time almost traditional in Protestant commentaries.
There is, however, a gradual progress in translation, which goes hand in hand with the progress of the understanding of the Bible. Jerome's Vulgate is an advance upon the Itala, both in accuracy and Latinity; the Protestant Versions of the sixteenth century are an advance upon the Vulgate, in spirit and in idiomatic reproduction; the revisions of the nineteenth century are an advance upon the versions of the sixteenth, in philological and historical accuracy and consistency. A future generation will make a still nearer approach to the original text in its purity and integrity. If the Holy Spirit of God shall raise the Church to a higher plane of faith and love, and melt the antagonisms of human creeds into the one creed of Christ, then, and not before then, may we expect perfect versions of the oracles of God.”

How Luther's theology may have influenced his translating