I don't feel badly at all throwing your errors back at you. Do you understand that when Jesus said, "It is finished.", he was speaking of making complete propitiation for the sins of the world? It is because he kept the law perfectly that he can be the sinless sacrifice for our sins and HIS righteousness is imputed to us, rather than having to stand on our own (which would condemn us for eternity). However, just because Jesus paid our penalty, it doesn't mean we are released from the responsibility to live holy, God-honoring lives and do the works God has prepared for us to do - not to BE saved, but because we ARE saved. That is why we are to obey God in those things He forbids or commands - you know, those ten commandments, for example.
So, when God says DON'T DO something, we should listen to Him and obey Him if we want to live happily in His grace. If he says don't cut yourselves for the dead, like pagans do, or don't make graven images and bow down to them, like pagans do, then DON'T do it. It can't get any simpler than that.
The whole discussion about cutting yourself for the dead began because someone with precious little knowledge of Scripture claimed that the Bible did not prohibit cutting oneself for the dead.
Before saying ridiculous things like this you need to poll the rest of the prot posse. Because that is word for word what they have said previously.
This means you aren't required to report to a celestial torture chamber to have red hot pokers jammed up your wazoo for several thousand years. Your sin is forgiven and you may enter directly into HIS presence.