The only way to overcome sinfulness is through the Holy Spirit. This is why Jesus who was a human, needed the Holy Spirit to help Him overcome sin for His entire life.
Since we can't do this or fail to do this, we now need to rely on the justification of Jesus. We no longer need to overcome sin, Jesus overcame it for us, and is our high priest who mediates for us to God since we can't. Though we are able to now have the Holy Spirit living inside us, who can help us avoid more sin than one without. But at this point we are avoiding sin to honor the father, not to gain any other status or reward or access to heaven. That comes only through Jesus.