Many thousands of people have been celebrating Mass with Pope Francis at a university campus in Kenya.
Pope Francis made a plea for traditional values, saying "the health of any society depends on the health of its families".
The Pope earlier urged Kenyans to work for peace and reconciliation on his first trip as pontiff to Africa, amid a rise in militant violence.
He arrived in Kenya on Wednesday, the first stop on a three-nation tour.
Crowds in the capital, Nairobi, waited in the rain at the University of Nairobi sports ground since the early hours of Thursday morning.
Wearing a robe embroidered to look like beads worn by the Maasai, Pope Francis told them: "Our faith in God's word calls us to support families in their mission in society, to accept children as a blessing for our world, and to defend the dignity of each man and woman, for all of us are brothers and sisters in the one human family."
He also spoke about abortion and the need for a caring society: "We are also called to resist practices which foster arrogance in men, hurt or demean women, and threaten the life of the innocent unborn."
Eyewitness: Benjamin Gakuru at the Mass
It was raining the whole night, but people slept in the rain in order to see Pope Francis.
The Pope was very happy to see thousands and thousands and thousands of people.
They came from all corners of Kenya and other parts of the region: DR Congo, Rwanda, Burundi and Tanzania.
At the Mass people were screaming and raising their flags, and everything was fantastic. People were very excited, excited, excited.
And Pope Francis appealed to young Kenyans "to shape a society which is ever more just, inclusive and respectful of human dignity".
He said they "should reject everything that leads to prejudice and discrimination".
'Be prophets of peace'
The hashtag #PapalMass has been trending on Twitter in Kenya as people have been reflecting on the event and the pontiff's message.
Gachiru said on Twitter that the mass "has reminded us of the beauty of simplicity and the power of ritual. The songs rang true to the Kenyan heart".
Amatikide Murunga said that she was "feeling very blessed and inspired by the Pope's visit to Kenya. [He is] truly a symbol of love".
Religion in sub-Saharan Africa:
- Christian population is 517 million (63% of total)
- Protestants make up more than half the number
- Catholics make up about a third
- Muslim population is 248 million (about 30% of total)
- 1.1 billion Christians expected by 2050
- 670 million Muslims expected by 2050
Source: US-based Pew Research Center 2011 survey
Before the Mass, Pope Francis met religious leaders from other faiths and other Christian denominations, who he said should be "prophets of peace" in a violent and hate-driven world.
Referring to attacks carried out by the militant Islamist group al-Shabab in Kenya, he said that God's name "must never be used to justify hatred and violence".
The Pope earlier said conflict and terrorism fed "on fear, mistrust, and the despair born of poverty and frustration".
A leading Muslim cleric in Kenya welcomed the visit, saying it gave hope to the "downtrodden in the slums".
The BBC's Anne Soy said that security was very tight for the Mass, but the pontiff played down security fears, joking that he was "more worried about the mosquitoes".
Pope Francis's five-day visit will also see him go to Uganda and Central African Republic, which has been hit by Christian-Muslim conflict.
He is later on Thursday expected to visit the headquarters of the UN Environment Programme.
He has already spoken of a "grave environmental crisis" facing the world, and said leaders needed to promote "responsible models of economic development".
Speaking on Wednesday he also made a veiled reference to corruption by calling on leaders to work with integrity and transparency, says the BBC's Joseph Odhiambo in Nairobi.
President Kenyatta has called on the Pope to pray that Kenya succeeds in its fight against corruption.
About 30% of Kenyans - including President Kenyatta - are baptised Catholics.