Evangelium Vitae Day celebrates a letter issued by Pope John Paul II in 1995 on threats to life such as abortion, euthanasia and the death penalty.
During his homily Sunday, Pope Francis said that people should accept the life provided by God, the Vatican Radio reported.
"All too often, people do not choose life, they do not accept the 'Gospel of Life' but let themselves be led by ideologies and ways of thinking that block life, that do not respect life," he said.
In his Angelus address following mass, Pope Francis recognized the beatification of Oduardo Focherini, who was killed in 1944 in a concentration camp for rescuing Jews.
He also greeted more than 100,000 participants who were in Rome for the Harley-Davidson rally, the Vatican Radio reported.
After the mass, Pope Francis blessed 1,400 motorcycles.