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(CNN) Pope Francis waded into the heart of a Kenyan shantytown Friday, spreading a message of acceptance and lashing out at the nation's elite for neglecting the poor.

Francis' visit to Kangemi aligned with his message of service to the poor during his three days in Nairobi.

In the sprawling slum filled with tin-roofed homes, he described injustices against the less fortunate as "new forms of colonialism."

The "dreadful injustice of social exclusion" leaves the poor with an unfair distribution of land, lack of access to infrastructure and minimal basic services, he said.

"Our world has a grave social debt toward the poor who lack access to drinking water because they are denied a life consistent with their inalienable dignity," the Pope said.

'We are so blessed'

Kangemi residents applauded his long-term focus on the downtrodden.

"Sometimes challenges in slums almost cause us to despair and some people give up working in slums," said Sister Mari Killeen, who works with the less fortunate.

"Your visit gives us courage. By coming here, you shine a light on the challenges. Your meeting with us gives us dignity."

When Francis weaved through the slum's narrow streets in his popemobile, crowds reached out to touch his hand as he waved from behind a clear protective covering.

Women ululated as children crooned Swahili welcome songs.

"I'm so happy, we are so blessed," said Magdalene Mwikali, 36, of Kangemi.

"He's left all those rich neighborhoods to come here," she said. "He's shown us we are important, that we matter, that God loves us, too."

Volunteer cleanup

Excited residents have prepared for his arrival for weeks.

Leading up to Friday, volunteer residents gathered to sweep littered streets and cover dirt roads with gravel, Mwikali said. Others perched Vatican and Kenyan flags on the road leading to the church in Kangemi.

Photos: Mother Teresa of Kenya: 'I'm not that fond of religions' Photos: Mother Teresa of Kenya: 'I'm not that fond of religions' Sister Mary Killeen, right, has been working in the slums of Nairobi, Kenya, for nearly 40 years. On Friday, she'll be addressing Pope Francis, who is on his first visit to the continent. Hide Caption 1 of 8 Photos: Mother Teresa of Kenya: 'I'm not that fond of religions' Killeen arrived from Ireland in 1976. In her early days, she said, close to half of Kenyan children were out of school -- and in parts of the city street children would sometimes steal people's clothes. "One day a group of these children approached me," Killeen said. But rather than steal from her as she anticipated, they asked her if she could help get their siblings into school. "They said, 'We're already thieves, but we don't want our siblings to have the same life that we had.' " Hide Caption 2 of 8 Photos: Mother Teresa of Kenya: 'I'm not that fond of religions' Since then, Killeen has developed dozens of educational programs and schools. She estimates she's assisted in the education of 300,000 children over the years. Hide Caption 3 of 8 Photos: Mother Teresa of Kenya: 'I'm not that fond of religions' "I can't walk any part of the city without meeting a past pupil," Killeen said. "Driving a car, in an office, as a manager somewhere, on the TV -- I turn on the TV and I see a past pupil from Nakuru giving out the news. It's very, very fulfilling work." Hide Caption 4 of 8 Photos: Mother Teresa of Kenya: 'I'm not that fond of religions' Most schools border poor communities. Killeen says land issues are a constant battle and school land is often encroached upon by developers. "The minute corruption goes up, poverty increases," she said. "Among the poor, you see an immediate effect." Hide Caption 5 of 8 Photos: Mother Teresa of Kenya: 'I'm not that fond of religions' Killeen helped found Songa Mbele, a school that cares for kids with disabilities. The mother of Zain Modeitsi, seen here, used to have to leave him at home alone in order to work. Hide Caption 6 of 8 Photos: Mother Teresa of Kenya: 'I'm not that fond of religions' Killeen assists in a physical therapy session for Zain, a 10-year-old who has severe cerebral palsy. "I've seen children walking who couldn't walk," Killeen said. "I've seen the deaf get help, and a little dumb child here who hasn't spoken yet but with help hopefully the child will speak. So it's like the gospel. You see the lame walk, the blind see, the dumb speak. So it's really wonderful to be part of that and to enable it. But we aren't doing as much as we should. It's a drop in the ocean." Hide Caption 7 of 8 Photos: Mother Teresa of Kenya: 'I'm not that fond of religions' "Religions, I'm not all that fond of them," Killeen said. "Religion is a way to help you reach love, understanding. You can call that God if you want. I'm not for piety, I'm for religion in action." Hide Caption 8 of 8

The presence of an international figure in their backyard drew some closer to the church.

"He has restored my faith. I have a role model and will practice his humility," said Regina Kimende, who came from a neighboring parish. "After seeing him today, I have decided my life is at the church. I'm starting all over."

Pope: Corruption eats you

Francis' last day in Kenya included meeting with youths at a Nairobi sports center, where he also held talks with bishops.

During his meeting with the youths, he addressed corruption, which is rampant in Kenya and has made headlines recently.

"It's not just in politics. It is in all institutions, including in the Vatican there are cases of corruption," he said.

"Corruption is something that eats you inside like sugar. It's sweet, we like it, it's easy. And then we end up sick and poor. So much sugar that we either end up being diabetic or own country ends up being diabetic."

He also called for equal distribution of wealth to ensure the disenfranchised are not at risk of getting radicalized.

In Uganda, then to the Central African Republic

Later Friday, he arrived in neighboring Uganda, kicking off the second leg of his Africa trip. His first stop there was at the state house in Kampala with President Yoweri Museveni, before meeting with officials, catechists and teachers.

A full day awaits Saturday that includes a visit to martyrs' shrines and celebrating Mass.

After two nights in Uganda, he'll head to the Central African Republic, the latter mired in a conflict in which Christians and Muslims are slaughtering one another.

First papal trip to Africa

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Francis' first papal trip to Africa started in Kenya on Wednesday, and has addressed other issues such as climate change and poaching.

He delivered a stern warning Thursday ahead of a key climate change conference in Paris next week. He urged nations to reach an agreement over curbing fossil fuel emissions, and work together to find solutions to environmental degradation.

"It would be sad, and I dare say even catastrophic, were particular interests to prevail over the common good," the Pope said.

But it was his comments on the pillaging of African resources that drew a louder response.

He urged Africans to demand an end to poaching, which "fuels political instability, organized crime and terrorism." The message reverberated with a nation where farming and tourism are a crucial part of the economy.

Unifying gesture

The Pope plans to visit a mosque in the Central African Republic, sending a powerful message of religious unity.

In the Central African Republic, a Muslim rebel group overthrew the Christian president two years ago, prompting brutal retaliatory attacks between Christian and Muslim militias.

Those attacks continue and have displaced hundreds of thousands of people.

Francis' predecessor, Pope Benedict, visited several countries in Africa. During his nearly three decades in the papacy, Pope John Paul II also made dozens of trips to the continent.