From American Magazine-
Faith is a journey guided by the Holy Spirit, who helps the church grow in understanding the sinful nature of once-accepted practices like slavery and the death penalty, Pope Francis said.
While people once even used religious reasons to justify practices such as slavery, the death penalty and "wars of religion," over time the Holy Spirit has deepened the church's understanding of the Gospel, the pope said on May 11 in his homily during morning Mass at Domus Sanctae Marthae.
Slavery "is a mortal sin; today we say this. Back then, some would say that this could be done because these people did not have a soul!" he said. The number of people enslaved today is "even more, but at least we know that it is a mortal sin. The same goes for the death penalty; for a time, it was normal. Today, we say that the death penalty is inadmissible."