Christ blood is not some divine act of camouflage so that we can continue to sin unpunished.
Christ blood does not only cover our sin, but it cleanses us. We are WASHED in the blood of our crucified lord. Our sins are not just masked with a big red ink splat. It is by his blood we are welcomed as sons and daughters of God. The Holy Spirit comes to live and reside with us, teaching us to walk with him and be like him.
We cannot continue to treat the spilt blood of Christ as if it were something that little red light flasher in the movie Men in Black that makes people forget what just happened. Christ blood does not make God forget our sins, his blood cleanses us from them, it allows us to enter a new life were we are to live righteously.