"16 Circumcise your hearts, therefore, and do not be stiff-necked any longer." -Deuteronomy 10
Cast away from you all corrupt affections and inclinations that hinder you from fearing and loving God. Mortify the flesh with its lustful desires. Throw off all filthiness and impurity that obstructs the work of the Word of God and the Holy Spirit in your heart. The circumcision of the heart makes it ready to yield to God.
In Matthew 5:29-30, Christ goes further urging us to cut off the hand or pluck out the eye if they are causing us to sin. It is better to cut off the hand or pluck out the eye than to indulge them in sin to the ruin of the soul. We must resolve to keep under the body, and to bring it into subjection; to live a life of mortification and self-denial; to keep a constant watch over our own hearts, and to suppress the first rising of lust and corruption there; to avoid the occasions of sin, to resist the beginnings of it, and to decline the company of those who will be a snare to us, though ever so pleasing; to keep out of harm’s way, and abridge ourselves in the use of lawful things, when we find them temptations to us; and to seek unto God for his grace, and depend upon that grace daily, and so to walk in the Spirit, as that we may not fulfil the lusts of the flesh; and this will be as effectual as cutting off a right hand or pulling out a right eye; and perhaps as much against the grain to flesh and blood; it is the destruction of the old man.
Do not be stiffnecked or obstinate (stubborn). Those who are obstinate continue in sin (2 Chronicles 28:22-23) refusing to change (Jeremiah 44:15-27).
Psalm 51:1-4, 10-12 (NIV)
A psalm of David. When the prophet Nathan came to him after David had committed adultery with Bathsheba.
"1 Have mercy on me, O God, according to your unfailing love; according to your great compassion blot out my transgressions. 2 Wash away all my iniquity and cleanse me from my sin. 3 For I know my transgressions, and my sin is always before me. 4....Against you, you only, have I sinned and done what is evil in your sight, so that you are proved right when you speak and justified when you judge. 10 Create in me a pure heart, O God, and renew a steadfast spirit within me. 11 Do not cast me from your presence or take your Holy Spirit from me. 12 Restore to me the joy of your salvation and grant me a willing spirit, to sustain me."