Calling these people "human bats," he said they are blinded by the light and only know how to move at night.
"And we too, when we are in sin, are in this state: we do not tolerate light. It is more comfortable for us to live in darkness; the light smacks us, shows us what we don't want to see," he stated.
The pope warned that the "eyes of the soul" get used to living in this darkness and lose all their sense of what the light is.
This state is clearly visible in the scandal and corruption of the world, he said, but "we too, when we are in a state of sin, in a state of estrangement from the Lord, we become blind and feel better in the darkness and go like this, without seeing, like the blind, moving as we can."
"Let the love of God, who sent Jesus to save us, enter us and 'the light that Jesus brings,' the light of the Spirit, enter us and help us to see things with the light of God, with the true light," he urged.
After Mass, Francis led Eucharistic adoration and benediction.
Before the start of Mass, he prayed for Europe, noting that unity is needed among nations right now and asking that Europe will have the "fraternal unity the founding fathers of the European Union dreamed of."
Pope Francis' prayer for Europe followed a day after he held a 45-minute phone conversation with French president Emmanuel Macron.
According to Macron's office, during the April 21 call the pope and Macron were in agreement on several issues regarding the COVID-19 pandemic response, including wanting to see unified action from the European Union.
Hannah Brockhaus is Catholic News Agency's senior Rome correspondent. She grew up in Omaha, Nebraska, and has a degree in English from Truman State University in Missouri.