Romans 7:5 Paul writes: Thanks be to God, through Jesus Christ our Lord! So then,
with my mind I serve the law of God, but
with my flesh I serve the law of sin.
There's nothing we can do to change our flesh. It is sold to sin. God doesn't relate to us in the flesh. We now live, move & have our being in God SPIRITUALLY! Even if we obey all the religious laws, our flesh cannot inherit anything spiritual, it'll never enter the Spiritual Kingdom of God.
If we're still trying to maintain holiness in our outward man, we have not yet understood the great thing God has done by placing His Son in us and is now this very moment making us more & more into the image of His Son Jesus Christ.
You can only purify yourself by getting rid of your old self. In other words, don't believe your logic or your own understanding anymore. Trust the Lord with all your heart & mind that He is reigning in you.