67. As co-workers of the bishops, priests are called by virtue of the sacrament of Orders to share in concern for the Church's mission: "The spiritual gift that priests have received in ordination prepares them, not for any narrow and limited mission, but for the most universal and all embracing mission of salvation 'to the end of the earth.' For every priestly ministry shares in the universal scope of the mission that Christ entrusted to his apostles." 134 For this reason, the formation of candidates to the priesthood must aim at giving them "the true Catholic spirit whereby they will learn to transcend the bounds of their own diocese, country or rite, and come to the aid of the whole Church, in readiness to preach the Gospel anywhere." ¹³⁵ All priests must have the mind and the heart of missionaries - open to the needs of the Church and the world, with concern for those farthest away, and especially for the non-Christian groups in their own area. They should have at heart, in their prayers and particularly at the Eucharistic Sacrifice, the concern of the whole Church for all of humanity.

Especially in those areas where Christians are a minority, priests must be filled with special missionary zeal and commitment. The Lord entrusts to them not only the pastoral care of the Christian community, but also and above all the evangelization of those of their fellow-citizens who do not belong to Christ's flock. Priests will "not fail to make themselves readily available to the Holy Spirit and the bishop, to be sent to preach the Gospel beyond the borders of their country. This will demand of them not only maturity in their vocation, but also an uncommon readiness to detach themselves from their own homeland, culture and family, and a special ability to adapt to other cultures, with understanding and respect for them." ¹³⁶

68. In his Encyclical Fidei Donum, Pope Pius XII, with prophetic insight, encouraged bishops to offer some of their priests for temporary service in the churches of Africa, and gave his approval to projects already existing for that purpose. Twenty-five years later, I pointed out the striking newness of that encyclical, which "surmounted the territorial dimension of priestly service in order to direct it toward the entire Church."137 Today it is clear how effective and fruitful this experience has been. Indeed, Fidei Donum priests are a unique sign of the bond of communion existing among the churches. They make a valuable contribution to the growth of needy ecclesial communities, while drawing from them freshness and liveliness of faith. Of course, the missionary service of the diocesan priest must conform to certain criteria and conditioning. The priests to be sent should be selected from among the most suitable candidates, and should be duly prepared for the particular work that awaits them.¹³⁸ With an open and fraternal attitude, they should become part of the new setting of the Church which welcomes them, and form one presbyterate with the local priests, under the authority of the bishop.¹³⁹ I hope that a spirit of service will increase among the priests of the long-established churches, and that it will be fostered among priests of the churches of more recent origin.