Sin enslaves.

"Jesus answered them, “Amen, amen, I say to you, everyone who commits sin is a slave of sin." (John 8: 34).

Sin enslaves.  Sin is addictive behavior. This is what makes the sinner a slave to his sin.  Here are examples of addictive behaviors:  pornography, alcoholism, anger, etc. This is what the Church teaches in this regard:
"Sin creates a proclivity to sin; it engenders vice by repetition of the same acts. This results in perverse inclinations which cloud conscience and corrupt the concrete judgment of good and evil. Thus sin tends to reproduce itself and reinforce itself, but it cannot destroy the moral sense at its root. (CCC 1865).

The price of freedom is fully paid by Jesus Christ.  "So if the son frees you, then you will truly be free."  (John 8: 36).  Only the disciples of Jesus Christ can  truly be free. How?
“If you remain in my word, you will truly be my disciples,  and you will know the truth, and the truth will set you free.”  (John 8: 31 - 32).

Praise to You, Lord Jesus Christ, King of endless glory.
"Blessed are they who have kept the word with a generous heart
and yield a harvest through perseverance."  (Luke 8: 15).

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