4. With this Instruction, therefore, the Missionary Dicastery wishes to provide norms to govern the sojourn of diocesan priests from mission territories who are living abroad. Such reasoning is warranted so that the young missionary Churches which are already short of personnel, and in particular of priests, are not deprived of ample apostolic strength that is absolutely indispensable for their Christian life and the ongoing development of evangelisation among those people who for the most part are not yet baptized⁶.