What was the purpose for the Holy Spirit being sent to us by the Lord ???
He was not sent to just seal us tell the day of redemption, for He was sent to guide us to keep us in the truth of the gospel and walking properly in the faith.
We are told over and over again in the NT that we are to abstain from sinning multiple times, and Apostle Paul even says those who are born again and walking by the Spirit have put to death their members in the flesh leading them to sin. Meaning you put those sinful ways aside to not do them any more.
You can not continue to walk in sinful nature as you did before you were born again or that shows no sign that the Holy Spirit does abide in you. Even Apostle John says if you say you love God but hate your brother the truth is not in you, and eternal life does not abide in you.
Paul, Peter, James, and John all taught that the walk(actions) in the faith can not be separated from the faith itself, or it is considered a dead faith if the person does not walk as taught and commanded.
When a believer sins they will repent and confess that sin and return to walking by the Spirit (in the Light), but if that person does not repent or confess but lets that sin lead them again controlling their life Apostle James says their soul will not be saved unless they return to the Lord.