It's a framework for understanding the spiritual aspect of reality. Certain details or terminology people get stuck on don't matter so much. The motivation is not to get to heaven and avoid hell (if you have a mature spirituality). It's being in harmony with the spiritual reality, for your benefit and the benefit of others. It's a relationship with God - the force that created reality.
I'm not suggesting all religions are good or equal or say the same thing; some are certainly better than others, as far as the spiritual insight and way of teaching/encouraging others to pay attention to their spiritual need. Most religions warn about false teachings, incidentally, for just the reason the OP mentions. False beliefs can be damaging to spirituality.
There are countless Christian religions with an enormous variation in beliefs. So which one do you refer to? I admit I find it annoying when people address "Christians" like it's a homogeneous group of people. Just as all religions are not equal, neither are all forms of Christianity, IMO.
My understanding is that "sin" is being out of harmony with the spiritual reality (and in some cases, the physical reality too). It's breaking a spiritual law of the universe, and there will be inevitable consequences, much as breaking a physical law results in consequences. These can be immediate consequences or stuff that builds up over time and does long-term damage (either on an individual or social level). Hell is not the consequence of sin. For people who believe in it (I don't believe in hellfire), hell is the consequence of an unrepentant attitude that signals rejection of God and essentially, an existence within the reality he created. We don't choose all sin, but we can and do choose permanent alienation from God.
You might be surprised at how many Christians don't believe in hellfire or an immediate afterlife. Even if they use the term "hell", it means something more like a permanent alienation from God.
Satan means "opposer" (if I recall correctly). Personally, I think it's useful to understand these forces as "active personalities" and not just abstractions. But that aside, Satan is basically a force opposing the spiritual reality. The lie is that we are physical beings ONLY (animals) and that we can be our own gods, alienated from The God (ie deciding good/bad for ourselves, not listening to the Creator). It's a lie because it denies the spiritual reality.
You don't have to die to find this out (and really, given the beliefs of many Christians, dying wouldn't give you any insight at all). You can experience being in harmony or opposed to the spiritual reality NOW.
In many Christian frameworks, when you operate in harmony with the spirit of God, then you manifest certain qualities - love, peace, joy, etc. When you oppose the spirit, then you manifest fleshy ("animalistic") qualities; these are often actions which indulge in physical instincts to a degree that they become harmful to yourself and others. Faith also comes into play, which partly means perceiving a pattern of how the spirit manifested before (in your life and for others), thus setting a precedent. It's not blind belief. What has to be developed is an ability to perceive, and much of religious framework is getting people to "see" spiritually and not just physically.
One more tangent - recently I was discussing Kierkegaard's distinction between the ethical and religious stages. Because of the change in connotations nowadays, I'd call ethical something closer to "religious" and religious "spiritual". Kierkegaard describes the ethical stage as a preoccupation with social rules that keep behaviors in check, which is what many think religion is for. They see it as a set of rules and beliefs one follows for particular outcomes. These people are not truly religious in a spiritual sense; they aren't mature yet. A fair amount of people do get stuck there. In contrast, the religious stage is about a personal relationship with God, and a spiritual maturity to the point of not needing the black and white rules of the ethical stage. It's a DYNAMIC. It's about harmonizing with an active force in reality - not just a force, but THE ultimate force. He basically describes what Jesus said in a far simpler way.
In short, the truth of it manifests through you right now.
