Benedict, who will inaugurate an important regional bishops' conference, said he was certain that the bishops will reinforce "the promotion of respect for life from the moment of conception until natural death as an integral requirement of human nature".
 
Poor turnout
 
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Thousands waited in the rain and cold for a glimpse of Benedict as he blessed them at the monastery where he is staying, but Al Jazeera's correspondent in Sao Paulo, Lucia Newman, said the turnout was relatively poor in the world's largest Catholic nation and in a city of 10 million.
 
The Vatican says Benedict will confront major challenges during his visit, such as the church's declining influence in Brazil, the exodus of Catholics to evangelical Christian churches, and efforts to expand access to abortion in the region.
 
In his first fully-fledged news conference since becoming pontiff in 2005, the pope was asked during his flight where he stood on the issue of excommunicating Catholic politicians approving abortion legislation and medical staff taking part in such procedures.
 
"The excommunication was not something arbitrary. It is part of the [canon law] code. It is based simply on the principle that the killing of an innocent human child is incompatible with going in Communion with the body of Christ.
 
"Thus, they [the bishops] didn't do anything new or anything surprising, or arbitrary.''
 
Church officials later said the pope might have thought the Mexican bishops had issued a formal declaration of excommunication for the legislators, something Norberto Rivera, the Mexican Cardinal, has said he has no intention of doing.
 
Benedict's spokesman, Federico Lombardi, said the pope was not setting a new policy and did not intend to formally excommunicate anyone - a rare process under church law that is separate from the doctrine of self-excommunication.
 
The pope was greeted by the Brazilian president
and first lady in Sao Paulo [Reuters]
"Since excommunication hasn't been declared by the Mexican bishops, the pope has no intention himself of declaring it," Lombardi said in a statement approved by the pope.
 
But Lombardi said politicians who vote in favour of abortion should not receive Communion – bread and wine that Catholics believe are transformed into the body and blood of Jesus Christ.
 
On the trip from Rome, Benedict said the exodus of Catholics for evangelical Protestant churches in Latin America was "our biggest worry".
 
"We have to become more dynamic," he said.
 
Opposition
 
But he may have his work cut out, with not just growing disenchantment but outright hostility towards the church.
 
Protesters held a vigil with signs stating "Jesus loves gay people" on Wednesday and called on the church to reform its stance on birth control, specifically on the use of condoms.
 
"A lot of people do not agree with the church's policies, we need to see a change in the church. We need to talk about this, that's why we are here," activist Clarissa Berez said.