Fidei Donum §11

¹¹ However, one must not allow the prodigious success of missionary effort, that We allude to here, to cause him to forget that "what still remains to be done demands an immense amount of work and countless workers." And although some might rashly conclude that once a Hierarchy has been established there is no further need for the work of the missionaries, yet We Ourselves are greatly troubled by Our "solicitude for all the Churches" of that vast continent.