We sin because we are sinners.
Our “free will” died in the Garden on the horrible day when our parents first sinned.
We still have free will.
Freedom to sin or to be obedient to God.
The only time that it was purely “ free will “ was before the fall, after that, what ever choice he makes is tainted , unless they are born again.
However Jesus said that you can not serve to masters, either you hate the one or love the other.
In the life of a christian, the spirit is rebirthed, but the flesh is still of the fallen nature.
Paul’s explanation in Romans chapter 7.
However, that Christian who is reborn in and with Christ is made justified, and given Christ’s gift of righteousness in the court of God judicially.
The spirit of a christian is saved, and is being sanctified, the mind is being renewed by the word of God , and the body, the flesh will be saved when Christ returns.
It’s a struggle with the flesh, the world, and the devil’s temptations every day that we live with until Christ returns.
That’s why the book of Romans says in chapter 8 that all creation grones, cries out to be released from this present corruption, that includes Christians in their flesh.