With the amazing naturalness of the things of God, the contemplative soul is filled with apostolic zeal. "My heart was warmed within me, a fire blazed forth from my thoughts." What could this fire be if not the fire that Christ talks about: "I have come to cast fire upon the earth, and what will I but that it be kindled?" An apostolic fire that acquires its strength in prayer. There is no better way than this to carry on, throughout the whole world, the battle of peace to which every Christian is called, to fill up what is lacking in the sufferings of Christ.
Jesus has gone up to heaven, as we have seen. But a Christian can deal with him, in prayer and in the Eucharist, as the twelve Apostles dealt with him. The Christian can come to burn with an apostolic fervour that will lead him to serve, to redeem with Christ, to sow peace and joy wherever he goes. To serve, that is what apostolate is all about. If we count on our own strength alone, we will achieve nothing in the supernatural order. But if we are God's instruments, we will achieve everything. "I can do all things in him who gives me strength." God, in his infinite goodness, has chosen to use inadequate instruments; and so, the apostle has no other aim than to let the Lord work in him and through him, to put himself totally at God's disposition, allowing him to carry out his work of salvation through creatures, through that soul whom he has chosen.
An apostle — that is what a Christian is, when he knows that he has been grafted onto Christ, made one with Christ, in baptism. He has been given the capacity to carry on the battle in Christ's name, through confirmation. He has been called to serve God by his activity in the world, because of the common priesthood of the faithful, which makes him share in some way in the priesthood of Christ. This priesthood — though essentially distinct from the ministerial priesthood — gives him the capacity to take part in the worship of the Church and to help other men in their journey to God, with the witness of his word and his example, through his prayer and work of atonement.
Each of us is to be ipse Christus: Christ himself. He is the one mediator between God and man. And we make ourselves one with him in order to offer all things, with him, to the Father. Our calling to be children of God, in the midst of the world, requires us not only to seek our own personal holiness, but also to go out onto all the ways of the earth, to convert them into roads that will carry souls over all obstacles and lead them to the Lord. As we take part in all temporal activities, as ordinary citizens, we are to become leaven acting on the dough.
Christ has gone up to heaven, but he has given to all honest human things a specific capacity to be redeemed. St Gregory the Great expresses this reality in a striking way: "Thus Jesus went away to where he had come from, and came back from the place he continued to dwell; for, in the very moment in which he went up to heaven, he brought together, by his activity, heaven and earth. On today's feast we should proclaim solemnly that the decree of our condemnation has been suppressed, and the judgment which made us subject to corruption has been lifted. That nature which heard the words, You are dust, and to dust you shall return, that same nature has gone up to heaven today with Christ."
And so I keep on repeating to you that the world can be made holy. We Christians have a special role to play in sanctifying it. We are to cleanse it from the occasions of sin with which we human beings have soiled it. We are to offer it to our Lord as a spiritual offering, presented to him and made acceptable through his grace and with our efforts. Strictly speaking, we cannot say that there is any noble human reality that does not have a supernatural dimension, for the divine Word has taken on a complete human nature and consecrated the world with his presence and with the work of his hands. The great mission that we have received in baptism is to redeem the world with Christ. We are urged on by the charity of Christ to take upon our shoulders a part of this task of saving souls.