Final answer:
Ambrose, the Bishop of Milan, along with the Cluniac reform movement, forbade the sale of church offices (simony) and pushed for clergy-elected bishops and priestly celibacy to purify the Church and reduce corruption, leading to conflict with European rulers.
Step-by-step explanation:
Ambrose, the Bishop of Milan, opposed certain practices within the Church based on the broader Cluniac reform movement, which sought to purify the Church and combat corruption. The sale of offices, known as simony, was condemned, and there was a push for the election of bishops by the clergy, independent from secular lords. Additionally, to address the issue of church positions being treated as inheritable fiefs, priests were encouraged to practice celibacy and not marry, thereby ensuring that church offices couldn't be passed down within families. These reforms were aimed at strengthening the spiritual integrity and autonomy of the Church, but also led to significant conflict with European rulers who were accustomed to exerting influence over church appointments.