From his commentary on I Corinthians iv:15 - There remains another question of greater difficulty: As Christ forbids us to call any one father upon earth, because we have one Father in heaven,(Matthew 23:9,) how does Paul dare to take to himself the name of father? I answer, that, properly speaking, God alone is the Father, not merely of our soul, but also of our flesh. As, however, in so far as concerns the body, he communicates the honor of his paternal name to those to whom he gives offspring, while, as to souls, he reserves to himself exclusively the right and title of Father, I confess that, on this account, he is called in a peculiar sense the Father of spirits, and is distinguished from earthly fathers, as the Apostle speaks in Hebrews 12:9. As, however, notwithstanding that it is he alone who, by his own influence, begets souls, and regenerates and quickens them, he makes use of the ministry of his servants for this purpose, there is no harm in their being called fathers, in re...