It is a mystery how the blood of Christ cleanses us from sin.
It is a mystery because we still sin. Yet we are called not to sin and there are times when we do not sin.
If I walk in the Spirit I do not fulfill the lust of the flesh. When I walk in the Spirit I essentially act without sin.
It is only without sin that I may enter his presence.
If I sin, he is faithful and just to forgive me and cleanse me of all unrighteousness. I repent and am then afforded the opportunity to continue in the Spirit.
Our freedom is not to be cover up for sin. To sin continually is to deny the power of the blood and risk being in a position of no return either because the conversion was never real or because it was lost.
How the blood of Christ is able to manage all of this is mystery. Let us simply be thankful for its working and endeavor to walk in the Spirit as much as possible.