John Calvin Commentary John 8:34

"Jesus answered them, Verily, verily, I say unto you, Every one that committeth sin is the bondservant of sin." — John 8:34 (ASV)

Every man who commits sin is the slave of sin. This is an argument drawn from contrary things. They boasted that they were free. He proves that they are the slaves of sin, because, being enslaved by the desires of the flesh, they continually sin. It is astonishing that men are not convinced by their own experience, so that, laying aside their pride, they may learn to be humble. And it is a very frequent occurrence today that the greater the load of vices by which a man is weighed down, the more fiercely he utters meaningless words in extolling free will.

Christ appears to say nothing more here than what was previously said by philosophers: that those who are devoted to their lusts are subject to the most degrading slavery. But there is a deeper and more hidden meaning; for he does not argue what evil men bring on themselves, but what is the condition of human nature. The philosophers thought that any man is a slave by his own choice, and that by the same choice he returns to freedom. But here Christ maintains that all who are not delivered by him are in a state of slavery, and that all who derive the contagion of sin from corrupted nature are slaves from their birth. We must attend to the comparison between grace and nature, on which Christ here dwells, from which it can be easily seen that men are destitute of freedom unless they regain it from some other source. Yet this slavery is voluntary, so that those who necessarily sin are not compelled to sin.