There is no such thing as a sin you do not know about. I mean there is, but unless you know it before you do it, sin is not acreddited to you. This is why Satan asked Eve to verbally confirm that this is the rule, and no matter the excuse, she's gonna do it- he trapped her with her own words, despite lies and temptation. Sin is KNOWING the good you ought to do and CHOOSING not to do it. If you know you should read the Bible, but choose not to know what God says in it, you sin, and even one sin not covered by Christ's blood keeps one out of heaven.
If you deliberately practice preplanned, premeditated sin, there no longer remains grace for you. Let's say you are fresh out of church, get home and continue fornicating, and then go to the store to buy cigarettes and alcohol for the week, cause you plan to get drunk, and you live in sin like this week after week, with no effort to stop sinning- then you are no longer in a safe spiritual state. You are not ridding yourself of sin, you are making provisions to sin in the future. You cannot continue to live in sin and expect Christ to cover sins you do on purpose with no desire or effort to stop.
As we try, and fail, Christ makes up the difference (grace). But Christ is not going to go up to an evil person, who gives no effort not to sin, and say they need do nothing, the He will do 100% on His part. If that were the case, the whole world would be saved. He did die to give the whole world the oppertunity to be saved, but most of them will not choose to be- for Jesus says wide is the road that leads to destruction (hell), and MOST enter through it.
We are being tested. There is something we must do on our part, and its more than simply believing God exists, just like demons do. We must die to sin and live in it no longer. If you VISIT sin in the moment of weakness, that is covered by grace (discipline on earth still applies). But if you are not just visiting, but are living there, in the same sin, on a regular basis, with no effort to change, grace does not cover that. You must die to sin, not wallow in it like a pig wallows in the mud.