St. Ambrose: "There must be a second purification"

“THERE is not one baptism only. One is that which the Church administers here by water and the Holy Ghost. Another is the baptism of suffering, whereby each is cleansed by his own blood. There is also a baptism at the entrance of Paradise. This last baptism did not exist in the beginning; but after the sinner was driven out of Paradise, God set there a fiery sword. . . . But though there be a purgation here, there must be a second purification there, that each of us, burnt but not burnt up by that fiery sword, may enter into the delight of Paradise. But this fire whereby involuntary and casual sins are burnt away . . . is different from that which the Lord has assigned to the devil and his angels, of which he says, Enter ‘into everlasting fire.’”

~St. Ambrose of Milan (c. 340-397): Explanation of Psalm 118, 3, 14-17.

St. Ambrose (detail), by Giovanni di Piamonte. 

Fresco, 1456-66; San Francesco, Arezzo.