You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Martin_Luther

Context:
Luther had published his German translation of the New Testament in 1522, and he and his collaborators completed the translation of the Old Testament in 1534, when the whole Bible was published. He continued to work on refining the translation until the end of his life. Others had translated the Bible into German, but Luther tailored his translation to his own doctrine. When he was criticised for inserting the word "alone" after "faith" in Romans 3:28, he replied in part: "[T]he text itself and the meaning of St. Paul urgently require and demand it. For in that very passage he is dealing with the main point of Christian doctrine, namely, that we are justified by faith in Christ without any works of the Law. ... But when works are so completely cut away – and that must mean that faith alone justifies – whoever would speak plainly and clearly about this cutting away of works will have to say, 'Faith alone justifies us, and not works'."

Question:
What did he work on refining until the end of his life?

the translation