Purgatory is like a purifying fire burning inside a person, a painful experience of regret for one's sins, Pope Benedict said.

"A soul stained by sin cannot present itself to God," the pope said Jan. 12 at his weekly general audience.

The pope spoke about purgatory in a talk dedicated to the life and mystical writings of St. Catherine of Genoa, a 15th-century married woman.

Married at age 16 to an older man with a gambling problem, she initially lived a worldly life, the pope said.

But after about 10 years, she was struck by the emptiness of her life in comparison to the greatness of God's love.

She began a "life of purification, which, for a long time, made her experience constant pain for the sins she committed and pushed her to impose penances and sacrifices on herself to demonstrate her love to God," the pope said.