Benedict was speaking at an open-air Mass on Beirut's Mediterranean seafront attended by 350,000 worshippers, according to the organisers' estimate, and leaders of Lebanon's Christian and Muslim communities including from militant Shi'ite group Hezbollah.
Peace between warring factions and among the many religious groups in the Middle East has been a central theme of his visit to Lebanon, along with his call to Christians not to leave the region despite war and growing pressure from radical Islamists.
Lebanon, torn apart by a 1975-1990 sectarian civil war, is a religious mosaic of more than four million people whose Muslim majority includes Sunnis, Shi'ites, Alawites and Druze. About one-third of the population is Christian.
"In a world where violence constantly leaves behind its grim trail of death and destruction, to serve justice and peace is urgently necessary," Benedict said yesterday at the Mass, at which he prayed for "Middle East servants of peace and reconciliaton".
"This is an essential testimony which Christians must render here, in cooperation with all people of good will," he said.
Benedict appealed on Friday for an end to the import of weapons into Syria, branding it a "grave sin" and saying a halt to the arms flow could help end the civil war.