Whereas some believe the gospel is found in the definition of what is a true Christian, the definition of a true Christian (among many defining characteristics) isn't just someone who believes they can be free from sin but someone who is indwelt by the Holy Spirit of God.
Unless one is born again (John 3:3) they can't see the kingdom of God let alone conquer their sins.
Desiring to be free from sin is obviously to be coveted but it's not the gospel.
Our being free from sin is a consequence of believing the true gospel which is that we believe that Christ is the Son of God, The Creator, who came into the world to die for our sins and by faith, God, the Holy Spirit indwells us by God's grace.
Having made Him Lord of our lives. We now walk in the Holy Spirit, purifying ourselves and growing in Christ to a mature stature towards the resembling of Christ's perfect moral standard, by God's grace and power.
We're saved by grace alone, through faith alone, and in Christ alone. It is a gift of God and not of our merit or "good" works.
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