Using strong language on one of his favourite themes, Pope Francis decried a plague of careerism among priests and urged them to renounce their personal ambitions for service to the Church.

"Careerism is a leprosy, a leprosy," the pope said June 6, in a speech to students from the school for future Vatican diplomats.

"Please, no careerism!"

All types of priestly ministry require "great inner freedom," the pope said, which calls for "vigilance in order to be free from ambition or personal aims, which can cause so much harm to the Church."

Priests must make the Gospel their priority, not self-fulfillment or public recognition.