35 All serious and upright human conduct is hope in action. This is so first of all in the sense that we thereby strive to realize our lesser and greater hopes, to complete this or that task which is important for our onward journey, or we work towards a brighter and more humane world so as to open doors into the future. Yet our daily efforts in pursuing our own lives and in working for the world's future either tire us or turn into fanaticism, unless we are enlightened by the radiance of the great hope that cannot be destroyed even by small-scale failures or by a breakdown in matters of historic importance. If we cannot hope for more than is effectively attainable at any given time, or more than is promised by political or economic authorities, our lives will soon be without hope. It is important to know that I can always continue to hope, even if in my own life, or the historical period in which I am living, there seems to be nothing left to hope for. Only the great certitude of hope that my own life and history in general, despite all failures, are held firm by the indestructible power of Love, and that this gives them their meaning and importance, only this kind of hope can then give the courage to act and to persevere. Certainly we cannot “build” the Kingdom of God by our own efforts—what we build will always be the kingdom of man with all the limitations proper to our human nature. The Kingdom of God is a gift, and precisely because of this, it is great and beautiful, and constitutes the response to our hope. And we cannot—to use the classical expression—”merit” Heaven through our works. Heaven is always more than we could merit, just as being loved is never something “merited”, but always a gift. However, even when we are fully aware that Heaven far exceeds what we can merit, it will always be true that our behaviour is not indifferent before God and therefore is not indifferent for the unfolding of history. We can open ourselves and the world and allow God to enter: we can open ourselves to truth, to love, to what is good. This is what the saints did, those who, as “God's fellow workers”, contributed to the world's salvation (cf. 1 Cor 3:9; 1 Th 3:2). We can free our life and the world from the poisons and contaminations that could destroy the present and the future. We can uncover the sources of creation and keep them unsullied, and in this way we can make a right use of creation, which comes to us as a gift, according to its intrinsic requirements and ultimate purpose. This makes sense even if outwardly we achieve nothing or seem powerless in the face of overwhelming hostile forces. So on the one hand, our actions engender hope for us and for others; but at the same time, it is the great hope based upon God's promises that gives us courage and directs our action in good times and bad.
Source: Spe Salvi (Vatican.va)