The Pope said that to participants in the council meeting of the superiors of the Pontifical Missionary Works and the World Congress of Fidei Donum Missionaries.
The meeting was held to commemorate the 50th anniversary of Pope Pius XII's 1957 encyclical "Fidei Donum."
Pius XII, "aware of the changing times and the arrival of new peoples and nations on the world stage, understood with far-sighted pastoral wisdom that new and providential horizons and missionary paths were opening for the announcement of the Gospel," Benedict XVI explained.
Along with traditional forms of missionary work, Pius XII also wished to encourage "another kind of missionary cooperation between the so-called ancient Christian communities and new or nascent ones in newly evangelized lands," the German Pontiff added. "The former would be urged to send priests to the 'young' and promising Churches to work with local ordinaries for a given period of time."
During these last 50 years, there has been an increase in the number of "fidei donum" priests.
"They left, along with religious and lay volunteers, for Africa and other parts of the world, at a great cost to their home dioceses," Benedict XVI explained.
The Holy Father expressed his gratitude, "in particular, to these our brothers and sisters, some of whom shed their blood to spread the Gospel."
"The exchange of gifts between old and new ecclesial communities has been an occasion of reciprocal enrichment and has aided the growth of the idea that we are all missionaries, that is, we are all involved -- albeit in different ways -- in proclaiming and bearing witness to the Gospel," the Pope said.
The missionary experience, he said, "leaves an indelible mark on those who participate in it and, at the same time, favors that ecclesial communion that makes the baptized feel like members of the one Church, the mystical body of Christ."
The Holy Father said he is well aware of the difficulties that exist today in the missionary field. He underlined the diminishing and aging clergy in those dioceses that at one time sent missionaries to far lands, which in the context of a "widespread vocations crisis" represent "a challenge to be met."
Despite this, Benedict XVI exhorted those present to "turn their gaze to the future with trust, giving a renewed and more authentic identity to the 'fidei donum' missionaries."
The Pope cited the words Jesus spoke when he sent his disciples to proclaim the Gospel to every corner of the world, "Behold, I am with you always, to the end of the age," saying that "this certainty must never leave us."
"The Lord of the harvest will not fail to send out laborers into his harvest, if we ask him with faith and in prayer and in the docile listening to of his word and his teachings," the Holy Father said.
Benedict XVI concluded his discourse by reiterating Pius XII's invitation to increase the number of Masses offered for the missions, saying he was certain that "the Lord, hearing our incessant prayers, will continue to bless the missionary activity of the Church with abundant fruits."