The fact is through our own self effort we are not able to not let sin reign in our mortal bodies. However, the Lord has given us a way that we can not let sin reign in our mortal bodies. When we are saved we die to the power of sin crucified with Christ through spiritual circumcision, we become dead to sin buried with Christ through spiritual baptism which cleanses us from all of our sin, then the Holy Spirit makes us alive to God through his quickening Holy Spirit where we become born again risen with Christ, and all of this is done by the gift of faith without works. Christ puts away all of our sins once and for all on the day of salvation. This is how we do not let sign reign in our mortal bodies. For he that is dead to sin is free from sin with no more sin debt, none of their sins are imputed anymore, God no longer remembers our sins, and God even inputs the righteousness of Christ to us. Where we become servants to righteousness and no longer servants to sin anymore. We become holy and righteousness to God through substitution atonement by faith alone with works through the work of God which is to believe in Jesus Christ.
Joh 6:28 Then said they unto him, What shall we do, that we might work the works of God?
Joh 6:29 Jesus answered and said unto them, This is the work of God, that ye believe on him whom he hath sent.
Ro 6:6 Knowing this, that our old man is crucified with him, that the body of sin might be destroyed, that henceforth we should not serve sin.
Ro 6:7 For he that is dead is freed from sin.
Ro 6:18 Being then made free from sin, ye became the servants of righteousness.
Ro 4:5 But to him that worketh not, but believeth on him that justifieth the ungodly, his faith is counted for righteousness.
Ro 4:6 Even as David also describeth the blessedness of the man, unto whom God imputeth righteousness without works,
Ro 4:7 Saying, Blessed are they whose iniquities are forgiven, and whose sins are covered.
Ro 4:8 Blessed is the man to whom the Lord will not impute sin.
2Co 5:17 Therefore if any man be in Christ, he is a new creature: old things are passed away; behold, all things are become new.
2Co 5:18 And all things are of God, who hath reconciled us to himself by Jesus Christ, and hath given to us the ministry of reconciliation;
2Co 5:19 To wit, that God was in Christ, reconciling the world unto himself, not imputing their trespasses unto them; and hath committed unto us the word of reconciliation.
2Co 5:20 Now then we are ambassadors for Christ, as though God did beseech you by us: we pray you in Christ's stead, be ye reconciled to God.
2Co 5:21 For he hath made him to be sin for us, who knew no sin; that we might be made the righteousness of God in him.
Ga 5:22 But the fruit of the Spirit is love, joy, peace, longsuffering, gentleness, goodness, faith,
Ga 5:23 Meekness, temperance: against such there is no law.
Ga 5:24 And they that are Christ's have crucified the flesh with the affections and lusts.
Col 2:9 For in him dwelleth all the fulness of the Godhead bodily.
Col 2:10 And ye are complete in him, which is the head of all principality and power:
Col 2:11 In whom also ye are circumcised with the circumcision made without hands, in putting off the body of the sins of the flesh by the circumcision of Christ:
Col 2:12 Buried with him in baptism, wherein also ye are risen with him through the faith of the operation of God, who hath raised him from the dead.
Col 2:13 ¶ And you, being dead in your sins and the uncircumcision of your flesh, hath he quickened together with him, having forgiven you all trespasses;
Col 2:14 Blotting out the handwriting of ordinances that was against us, which was contrary to us, and took it out of the way, nailing it to his cross;
Col 2:15 And having spoiled principalities and powers, he made a shew of them openly, triumphing over them in it.
Heb 8:12 For I will be merciful to their unrighteousness, and their sins and their iniquities will I remember no more.
Heb 9:26 For then must he often have suffered since the foundation of the world: but now once in the end of the world hath he appeared to put away sin by the sacrifice of himself.