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Grace is not 'free'. Read Romans 6. And another thing, he told the woman that the Pharisees brought to him "go and sin no more". She had to repent, which has a definition that you cannot justify sin with; to repent means to 'turn away' from sin, not just let Jesus's death pay for it.
We do not repent of sin to save ourselves. We believe Jesus died for all our sins and we are saved by what He did and not by what we do. Romans 11:6 It is all grace, not works. We can not save our selves.
Ephesians 2:8-9 For by grace ye are saved, through faith, and that not of yourselves, it is the GIFT of God, not of works, lest any man should boast.
We have nothing to boast in because it is a free gift from God. We did nothing for it. Jesus paid it all and we paid 0. It is free. Amazing grace.
Bible repentance for salvation is to change your mind and believe the gospel. That Christ died for all our sins. It means to quit trusting in what you do to save yourself, and trust Jesus finished work on the cross to save you.
Repenting of sin saves no one. Turning from sin to God saves no one. Believing that Jesus died for all our sins is what saves us. Jesus is grace. His grace is sufficient for all our sin. Salvation is a free gift from God. Romans 6:23 For the wages of sin is death, but the gift of God is eternal life, through Jesus Christ our Lord.