Moral relativism “endangers the coexistence of peoples,” Pope Francis told diplomats, and said a common ethics based on human nature is an indispensable condition for world peace.

The pope made his remarks to the Vatican diplomatic corps in the Apostolic Palace’s Sala Regia, the vast hall where popes traditionally receive Catholic monarchs.

The Vatican currently maintains diplomatic ties with 180 states, as well as the European Union, the Sovereign Military Order of Malta and the Palestine Liberation Organization.

Saudi Arabia and Afghanistan, which do not exchange ambassador with the Holy See, sent representatives to the Mass.