The Archdiocese of San Francisco tweeted about a homily Archbishop Salvatore Cordileone made on Sunday as the nation marked the 21st anniversary of the attacks on 9/11.

“Dear police officers, firefighters, sheriffs and park rangers of our city of San Francisco: it is an honor for us to host you here… for this Mass in which we thank you for the sacrifices you make for us, sacrifices mostly which we do not even see,” Archbishop Salvatore Cordileone said on Twitter.

He was one of many Church leaders to express appreciation for the work so many did, even when it meant they put themselves in harm’s way.

Elsewhere, the U.S. Conference of Catholic Bishops (USCCB) posted a tweet calling to mind a special prayer offered in the past.

“As we remember September 11, 2001, let us reflect on Pope Francis' Prayer of Remembrance at Ground Zero in 2015,” the tweet said. The tweet shared the opening of Pope Francis’ prayer that he made at the Ground Zero Memorial during his visit to New York in September, 2015. The full prayer can be read here.

Catholic leaders have regularly reflected on the lessons people could learn from the attacks.

One of the first messages was issued on Nov. 14, 2001, when the USCCB released a pastoral message document titled “Living With Faith and Hope After September 11.” In it, the USCCB quotes the Beatitudes (Mt. 5:4,6,7,9) and says, “We offer words of consolation, criteria for moral discernment, and a call to action and solidarity in these troubling and challenging times.”

The bishops used the message to honor the men and women, firefighters, police, chaplains and others who sacrificed their lives during and after the attacks. The document reminds people to respond with faith and justice, and to further understand the role that religion can play in politics and terrorism. The USCCB emphasized the nation’s commitment to the common good, in unity with a determination to come together and defend America from all future threats, according to the pastoral message.

Last year, on the 20th anniversary, the Pillar released an article titled “The Catholic Church and 9/11” that offers stories and testimonials from that day. It mentions Pope St. John Paul II’s address about the attacks on Sept. 12, 2002. “Christ’s word is the only one that can give a response to the questions which trouble our spirit,” Pope St. John Paul II said at the time. “Even if the forces of darkness appear to prevail, those who believe in God know that evil and death do not have the final say.” 

A prayer service was held at St. Patrick’s Cathedral in New York City in 2011 on the 10-year anniversary. “We decided to have exposition of the Blessed Sacrament,” a Brooklyn pastor said at that service, according to the Pillar. “We decided to have exposition of the Blessed Sacrament. People flocked to the church… We held many funerals for police and fire persons who gave their lives.”

On a different note, a video features Father Brian Jordan, a Franciscan Friar, tells the story of the Ground Zero Cross that survived the attack despite being in the middle of so much destruction.