78 Among the forms of sharing, first place goes to spiritual cooperation through prayer, sacrifice and the witness of Christian life. Prayer should accompany the journey of missionaries so that the proclamation of the word will be effective through God's grace. In his Letters, St. Paul often asks the faithful to pray for him so that he might proclaim the Gospel with confidence and conviction. Prayer needs to be accompanied by sacrifice. The redemptive value of suffering, accepted and offered to God with love, derives from the sacrifice of Christ himself, who calls the members of his Mystical Body to share in his sufferings, to complete them in their own flesh (cf. Col 1:24). The sacrifice of missionaries should be shared and accompanied by the sacrifices of all the faithful. I therefore urge those engaged in the pastoral care of the sick to teach them about the efficacy of suffering, and to encourage them to offer their sufferings to God for missionaries. By making such an offering, the sick themselves become missionaries, as emphasized by a number of movements which have sprung up among them and for them. The solemnity of Pentecost - the beginning of the Church's mission - is celebrated in some communities as a "Day of Suffering for the Missions."
Source: Redemptoris Missio (Vatican.va)