Pope Francis is willing to tell US President Donald Trump in person that building border walls is wrong.
The summit hopes to tackle paedophilia scandals and for bishops to have clear ideas on how to spot and deal with abuse.
The scandals involving nuns broke as the Catholic church struggled with a wave of cases involving paedophilia among priests worldwide.
Pope Francis signed a document on Monday, "Document on Human Fraternity" to cease using religion as a force "to incite hatred, violence, extremism and blind fanaticism, and to refrain from using the name of God to justify acts of murder, exile, terrorism and oppression."
More than 120,000 worshippers packed Zayed Sports City stadium and its surroundings in Abu Dhabi, the capital of the United Arab Emirates, to see the pope.
This is not the first time the Argentinian pope has appealed to European leaders to open their borders.
The resignations are the latest in a series of key staff changes within the pope's communications office.
The new clinic with three visiting rooms will be open three days a week and will be staffed by volunteer doctors from the Vatican medical services and Rome hospitals.
The Roman Catholic Church's position is that homosexual acts are sinful and the pontiff's stance on homosexuality is not new.
Both were stripped of their priesthood "as a consequence of overt acts of abuse against minors".
Cardinal Wuerl had offered to resign after facing strong criticism over a report detailing mass sexual abuse cases when he was a bishop in Pennsylvania.
Archbishop Vigano said the pope knew for years about sexual misconduct by McCarrick with adult male seminarians but did nothing about it.
Vatican's statement stated that both abuse and its cover-up can no longer be tolerated.
Father Fernando Karadima was defrocked, or "reduced to the lay state" by the pope on Thursday, a move the Vatican called "exceptional" and done "for the good of the Church".
A Chinese Foreign Ministry spokesman said China was sincere about wanting better relations with the Vatican and that the bishops' agreement was an important step forward.
Francis will honour victims of Soviet-era persecution during a visit to a museum in the former KGB building in Vilnius, where regime opponents were tortured and killed.
A sweeping grand jury report released in August revealed credible allegations against more than 300 predator priests and identified over 1,000 victims of child sex abuse covered up for decades.
The Argentinian pontiff's visit will be brief but is part of a wider campaign he has been waging against organised crime.
The Catholic Church worldwide is reeling from crises involving sexual abuse of minors. Surveys show plummeting confidence in the Church the United States, Chile, Australia, and Ireland where the scandal has hit hardest, as well as in other countries.
The accusations shook the US Church, following a report that found 301 priests in the state had sexually abused minors over the past 70 years.
Pope Francis told newly ordained bishops that they must reject all forms of abuse and work in communion to fight the clerical culture that has fueled sex abuse and cover-up scandals.
The Syrian province of Idlib and surrounding areas are the last major enclave held by rebels opposed to Syrian President Bashar al-Assad.
The pope has sided with those who believe global warming is at least partly man-made
Archbishop Carlo Maria Vigano has gone into hiding since an 11-page statement in which he alleged the pope knew about sexual misconduct by an American cardinal and did nothing about it.