Almost everything unusual about Mit Brennender Sorge follows from the problem of delivery. An encyclical is normally composed in Latin, published in the Roman gazette and circulated openly. This one was drafted in German, at the urging of the German bishops who came to Rome in January 1937, principally by Cardinal Michael von Faulhaber of Munich with revisions by Cardinal Pacelli, the Secretary of State who had negotiated the 1933 concordat and who would become Pius XII.
Copies were carried into Germany by hand, set in twelve printing houses, and distributed to parishes by couriers on foot and by bicycle. On Palm Sunday, 21 March 1937, it was read from Catholic pulpits across the country before the authorities knew it existed. The state's response was immediate: presses were seized and closed, staff were arrested, and possession of the text was treated as a criminal act.
The text itself is careful. It begins from the concordat and lists what has been done in breach of it: the dissolution of Catholic youth organisations, interference with confessional schools, the harassment of clergy and press. It then turns to doctrine, and rejects the elevation of race, of a people, of the state or of any other created value into an absolute, and the reduction of God to a national deity. It never names Adolf Hitler, the National Socialist party or the regime.