Setting the tone for his papacy, Pope Benedict today urged humanity to re-discover God if it wanted to transform the world's "deserts" of poverty, pain and privation into gardens of peace and progress.
Speaking in Italian at his inaugural Mass in the splendour of a sunlit St Peter's Square, the new pontiff called himself "a weak servant of God" and appealed for prayers to help him in the "enormous task that truly exceeds human capacity".
"My real programme of governance is not to do my own will, not to pursue my own ideas, but to listen, together with the whole Church, to the word and the will of the Lord," he said to loud applause from a crowd estimated at half a million people.
Three weeks after the death of John Paul, pilgrims and patriarchs, presidents and priests again packed the cobbled expanse in front of St. Peter's Basilica for the open-air service - the final rite in the papal transition.
Security was again tight, as it was for the funeral mass for John Paul. Rome shut its airspace, blocked off roads and had anti-aircraft missiles and a NATO plane guarding against attack.
Applause from a flagwaving crowd that included many from the Pope's native Germany interrupted the speech at least 30 times.
Benedict, who at 78 is the oldest man to be elected Pope for three centuries, takes over the Church at a time of dwindling congregations in Europe and stiff competition from evangelical sects for followers in the developing world.
In his first official sermon as the 265th Pope, the former Cardinal Joseph Ratzinger, a German, re-committed the Church to the search for Christian unity and continued dialogue with Jews.
But his main focus was on what he called a world of alienation, suffering and death that he said had become a spiritual wasteland and on leading a Church he said was still very much alive and able to grow.
"There are so many kinds of desert. There is the desert of poverty, the desert of hunger and thirst, the desert of abandonment, of loneliness, of destroyed love," the Pope said.
"There is the desert of God's darkness, the emptiness of souls no longer aware of their dignity or the goal of human life. The external deserts in the world are growing, because the internal deserts have become so vast.
"Therefore the earth's treasures no longer serve to build God's garden for all to live in, but they have been made to serve the powers of exploitation and destruction," he said.
Only by turning to God could modern man emerge from what he called "the salt waters of suffering and death ... a sea of darkness without light."