Pope Benedict XV recalled the great Apostles of the Gospel who contributed much to the Expansion of Missions . He reviewed the recent history of the missions and stated the purpose of the Apostolic letter. The encyclical first turned to the bishops and superiors in charge of the Catholic missions, noting the need to train local clergy. Catholic missionaries are reminded that their goal is a spiritual one, which must be carried out in a self-less way. 
The Pope underlined the necessity of proper preparation for the work in foreign cultures and the need to acquire language skills before going there. He requests a continued striving for personal sanctity and praises the selfless work of female religious in the missions. Mission is not only for missionaries, all Catholics must participate, through their Apostolate of Prayer, by supporting vocations, and by helping financially  The encyclical concludes by pointing out several organizations which organize and supervise mission activities within the Catholic Church 
The war being over, Pope Benedict repeats the biblical mandate to the ends of the earth and preach the gospel. He recalls the examples of Francis Xavier in India and Bartolomé de las Casas in the Americas and others to show what individuals can do in the service of God. Many missionaries died as martyrs for their faith and many live like saints.  He is also impressed with what has been achieved so far
- Anyone who studies the facts of this great saga cannot help being profoundly impressed by them: by all the stupendous hardships our missionaries have undergone in extending the Faith, the magnificent devotion they have shown, and the overwhelming examples of intrepid endurance they have afforded us. And to anyone who weighs these facts the realization must come as a shock that right now, there still remain in the world immense multitudes of people who dwell in darkness and in the shadow of death. According to a recent estimate, the number of non-believers in the world approximates one billion souls. 
The most important point to Benedict is the development of local clergy, for any one who has charge of a mission, his special concern must be, to secure and train local candidates for the sacred ministry:
- In this policy lies the greatest hope of the new churches. For the local priest, one with his people by birth, by nature, by his sympathies and his aspirations, is remarkably effective in appealing to their mentality and thus attracting them to the Faith. Far better than anyone else he knows the kind of argument they will listen to, and as a result, he often has easy access to places where a foreign priest would not be tolerated.
- [http:/ www.svdcuria.org/public/mission/docs/encycl/mi-en.htm - Complete text of the Apostolic Letter Maximum Illud of Pope Benedict XV .]