Well, I don’t really believe these particulars anymore, so I’m trying to go more off of what I was taught. I don’t remember the supposed efficacy of sacrifices prior to Jesus’s crucifixion so I can’t really answer to that. For afterward though, it’s not exactly a one time thing, we’re still expected to try to well and to ask for forgiveness, we would just not have to have a sacrifice anymore. For instance, look at Catholics, they still do confessionals and all. So it’s not exactly just a one-time thing, it’s not like you just accept the sacrifice and ask for forgiveness once then do whatever. It’s supposed to be an ongoing process of realizing sin, sincerely asking for forgiveness, and trying to live more Christ-like constantly.
The best analogy I can really think of would be like comparing a bucket of water to faucet. If I’m washing my hands, I can only use the bucket of water so much before the water gets filthy enough that it won’t clean my hands anymore, so I have to go fetch more. But every time I want to wash my hands with a faucet, there is effectively an endless supply of clean water.
One thing I forgot that might clarify is that I was also taught that during his three days of death, Jesus descended into hell. I never believed that, I don’t even believe in hell, so I’m not sure if that clarifies or muddies the point.
I don’t look at it as a replacement, I think that’s where the whole descended in to hell thing came from people people didn’t really get the other aspect. I don’t look at it as sin requires death, it’s more that sin IS death. That is, sin is doing things that separate us from perfection, that is exactly what spiritual death is. It’s sort of like looking at a smoker and lamenting that it’s unfair that they end up living shorter lives and having lung cancer and stuff; it’s not a punishment for smoking, its a direct consequence of smoking.
When I was a kid, and I’m sure most of us have similar stories, on weekends I’d go outside and play, and mom would mom the floor and vacuum the carpets and all and when I’d come inside she’d make me take my shoes off. It wasn’t a conditional of “well, if your shoes are clean enough it’s okay”; it didn’t matter if I was running around in the mud or on the clean pavement, I had to take them off. I couldn’t make an argument about how clean my shoes may or may not be, even if I had been on the clean pavement, it was true that my shoes were still dirtier than a freshly mopped kitchen floor. That floor was, for the sake of this analogy, perfectly clean, and even if my shoes were nearly clean, I still couldn’t walk in the house wearing them.
My point is, we see degrees of sin and compare them because we’re comparing them to ourselves, but relative to God, we all fall short, even the least sinning human ever is still going to fall short of perfection, just like even the cleanest kid in the neighborhood will still have to take off his shoes before walking on that freshly mopped kitchen floor.