The passage you quoted in 1 John is directed to those who are members of the body of Christ. This is referring to their walk after becoming a child of God. The question is at what point does the individual sinner come in contact with the blood of Christ.
At the moment he becomes “in Christ”. I think we are talking past each other. Here are the three Salvation models as I know them
One Saved Always Saved - primarily Baptist. You are Saved at the moment you decide for Christ. You can die in a brothel shootout after having never darkened the door of a church after your conversion and still go to Heaven.
Fall from Grace - primarily Methodist and Pentacostal. If you leave the church after conversion and go work in a brothel, your Salvation falls off. You return to an unSaved state and will go to Hell if you do not turn around.
Perseverence of the Saints - Calvinist - If you go to work in the brothel after conversion, you were never Saved. You just thought you were Saved. If you die unSaved, you were never one of the Elect.
I am off to work. Be back later