ROME, Italy (AP) – Pope Benedict XVI pledged yesterday to resist attempts to water down Vatican teaching, indicating he will uphold Pope John Paul II’s unwavering stands against abortion and euthanasia and will work to guarantee obedience to Church doctrine.

Benedict outlined his vision of his papacy in a homily during a ceremony in which he took his place on a marble-and-mosaic throne in the ancient Roman basilica of St John in Lateran. The ceremony is the last in Benedict’s formal assumption of the papacy.

His 30-minute homily, read in a calm, confident manner, reflected his experience guarding doctrinal orthodoxy and defending papal authority for two decades under John Paul.

The pope “must not proclaim his own ideas, but ever link himself and the Church to obedience to the word of God, when faced with all attempts of adaptation or of watering down, as with all opportunism,” Benedict said.

“That’s what Pope John Paul II did, when … faced with erroneous interpretations of freedom, underlined in an unequivocal way, the inviolability of human beings, the inviolability of human life from conception to natural death,” Benedict said.

“Freedom to kill is not a true freedom but a tyranny that reduces the human being into slavery,” the pontiff said to ringing applause from the congregation.

In Vatican teaching, references to defence of life “from conception to natural death” refer to its bans on abortion and euthanasia.

Marshalling his arguments, Benedict said: “The pope isn’t an absolute sovereign, whose thoughts and desires are law. On the contrary – the ministry of the pope is to be the guarantor of obedience to Christ and to his word.”

In his former role of Vatican’s watchdog on doctrine, he earned a reputation as a strict interpreter of Church teaching who silenced dissident theologians.

The installation as Bishop of Rome traditionally takes place in the ancient basilica, which the Vatican describes as the “mother and head of all the churches of the city of Rome and of the world.”

Arriving at and leaving the ceremony, Benedict was cheered by thousands of Romans who lined a boulevard as he drove by in an open-topped black limousine. Standing and waving to the crowd as the car slowly travelled down the street, the pope seemed intent on establishing a rapport with his flock.

“Dear Romans, I am now your bishop,” Benedict said, concluding his homily. The first Christian basilica to be erected in Rome, St John’s was founded by the Emperor Constantine. Its original foundations were raised in the early 5th century.

Before returning to the Vatican, Benedict visited another important Rome basilica, St Mary Major. The basilica’s archpriest, Cardinal Bernard Law, stood outside the church to greet the pope, kissing Benedict’s hand and genuflecting before the pontiff went inside to place flowers before an icon of the Virgin Mary.

Law was assigned to the basilica by John Paul after the cardinal was forced to resign as archbishop of Boston because of his handling of the clergy sex abuse scandal.

As Benedict walked briskly down St Mary Major’s centre aisle, faithful thrust their hands at him and he stopped to shake many of them.

Benedict seems intent on shedding his image he earned while working in the doctrinal office as a retiring, deskbound, cold-natured churchman.

In his homily, Benedict said a pope must be aware of being a “fragile and weak man” to whom God grants the “strength to confirm his brothers in the faith and keep them united”.