"There is always a risk... Of giving in to that sort of 'bourgeoisie of the spirit and life' which drives one to recline, to seek out a comfortable and tranquil life," he told ambassadors gathered at the Vatican from all over the world.
"Giving in to such a worldly spirit exposes us pastors in particular to ridicule. We would perhaps be applauded by some, but those who seem to approve of us would criticise us behind our backs," he added.
"Be careful that the candidates are pastors who are close to the people... Are mild-mannered, patient and merciful; that they love poverty... (and lead) simple and austere lives," he said.
Beware of those who have a "princely psychology" and above all "be careful that they are not ambitious, that they do not seek the episcopate," he added.
The meeting between Francis and the ambassadors was unusual. It had been organised by the pope's predecessor Benedict XVI, who had been accused of having an excessively formal relationship with the ambassadors, with whom he rarely met.