In the rousing 55-minute speech, the pope also repeated the church's apology for its role in colonialism of the Americas.
The cross was created by a Jesuit martyr, who was assassinated in 1980 after being active in Bolivia's pro-democracy movement.
The Eucharist calls people to give all they are and have to God, seek his blessing and then take his love to the world, Pope Francis said in Bolivia.
Pope Francis also praised Bolivia's efforts to include all its citizens in the country's economic, political and social life.
Belfries and spires poke the sky in this ramshackle city of impromptu developments, rutted roads and brick buildings, billed by locals as one of the highest in the world at more than 13,000 feet above sea level.
In the Villa Adela neighborhood, an onion dome towers over the Cuerpo de Cristo parish -- easily visible from the runway of the nearby international airport, where Pope Francis is scheduled to land Wednesday for a brief visit to El Alto and nearby La Paz.
"Those who choose the path of service ... are always at others' service. Not a moment belongs to them," the pope told a gathering of clergy in Ecuador.
The outcome of May's same-sex marriage referendum in Ireland and the decision of the U.S. Supreme Court on the same issue clearly show the extent to which Western society is abandoning many of its Christian legal foundations, said Australian Cardinal George Pell, prefect of the Vatican's Secretariat for the Economy.
In his address at the Fota VIII International Liturgy Conference in Cork, Pell called the Irish referendum "a victory for John Stuart Mill and utilitarianism."
A well-intentioned argument is developing among some Westerners, urging the evacuation of Christians from the Middle East. These Westerners reason that because no one will defend the Middle Eastern Christians, they should be resettled elsewhere.
Pope Francis tied together the Christian proclamation of faith with Ecuadoreans' centurieslong struggle to stop exploitation of their resources and their very selves.
Residents of Villa 21-24, a slum on the south side of the Argentine capital, hold fond memories of Pope Francis.