At the centre of the Church's worship is the notion of "sacrament". This means that it is not primarily we who act, but God comes first to meet us through his action, he looks upon us and he leads us to himself. Another striking feature is this: God touches us through material things, through gifts of creation that he takes up into his service, making them instruments of the encounter between us and himself. There are four elements in creation on which the world of sacraments is built: water, bread, wine and olive oil. Water, as the basic element and fundamental condition of all life, is the essential sign of the act in which, through baptism, we become Christians and are born to new life. While water is the vital element everywhere, and thus represents the shared access of all people to rebirth as Christians, the other three elements belong to the culture of the Mediterranean region. In other words, they point towards the concrete historical environment in which Christianity emerged. God acted in a clearly defined place on the earth, he truly made history with men. On the one hand, these three elements are gifts of creation, and on the other, they also indicate the locality of the history of God with us. They are a synthesis between creation and history: gifts of God that always connect us to those parts of the world where God chose to act with us in historical time, where he chose to become one of us.
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Read completely the homily Benedict XVI delivered at the Chrism Mass held at St. Peter's Basilica at http://www.zenit.org/article-28828?l=english