Because belonging to the church (being a church official such as a priest or a bishop) esentially meant you were given education (not common or at all present in those times) and a good position with a pay. You also exerted a lot of power in your local or regional community as church officials were considered to have been influential figures in medieval ages.
to decide domestic and foreign policies.
On August 23, 1939–shortly before World War II (1939-45) broke out in Europe–enemies Nazi Germany and the Soviet Union surprised the world by signing the German-Soviet Nonaggression Pact, in which the two countries agreed to take no military action against each other for the next 10 years.