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 came to understand justification as entirely the work of God. This teaching by Luther was clearly expressed in his 1525 publication On the Bondage of the Will, which was written in response to On Free Will by Desiderius Erasmus (1524). Luther based his position on predestination on St. Paul's epistle to the Ephesians 2:8–10. Against the teaching of his day that the righteous acts of believers are performed in cooperation with God, Luther wrote that Christians receive such righteousness entirely from outside themselves; that righteousness not only comes from Christ but actually is the righteousness of Christ, imputed to Christians (rather than infused into them) through faith. "That is why faith alone makes someone just and fulfills the law," he wrote. "Faith is that which brings the Holy Spirit through the merits of Christ." Faith, for Luther, was a gift from God; the experience of being justified by faith was "as though I had been born again." His entry into Paradise, no less, was a discovery about "the righteousness of God" – a discovery that "the just person" of whom the Bible speaks (as in Romans 1:17) lives by faith. He explained his concept of "justification" in the Smalcald Articles:

Question:
Where did Luther explain his idea of justification?

Smalcald Articles