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:
In the summer of 1521, Luther widened his target from individual pieties like indulgences and pilgrimages to doctrines at the heart of Church practices. In On the Abrogation of the Private Mass, he condemned as idolatry the idea that the mass is a sacrifice, asserting instead that it is a gift, to be received with thanksgiving by the whole congregation. His essay On Confession, Whether the Pope has the Power to Require It rejected compulsory confession and encouraged private confession and absolution, since "every Christian is a confessor." In November, Luther wrote The Judgement of Martin Luther on Monastic Vows. He assured monks and nuns that they could break their vows without sin, because vows were an illegitimate and vain attempt to win salvation.

Question:
How did Luther describe the mass that was viewed as sacrifice?

condemned as idolatry