I find it helpful to understand that unlike some religions our books are not the direct word of God. This means that flawed humans, especially men, have had a hand in them.
It's also helpful to understand that there are a vast number of different Christianities, currently, and combining those in the past.
The idea that a religion is fixed is a fallacy, it changes as society does.
My own personal belief is that the Gospels are the most important thing. The other stuff has some good bits, but it's important to recognise flaws and allegory etc.
Our version of Christianity is that it's what Jesus said that is important, how he lived, his message. Even though those were filtered through years before they were formalised, and some accounts were ignored, there has to be a truth at the heart of it. That really what we should be doing consists of love, love and kindness for everyone regardless, for we are all humans and in this together.
My view really is that we are God's children, and like children the real world is revealed a little at a time. So as science makes advances we understand more of our physical world. So we go from God as a man in the sky who created this one world, to a God that created many and is of a form we have no understanding of... yet.
And as for grace, well really, I think part of it is to stop us getting too big for our boots. Sure I give plenty to charity and treat everyone like they're a human being because they are, but to use that as a basis for assuming I'm somehow better. That feels wrong. God has shown he can do the ultimate in forgiveness, but that is abstract to us. What we can know is that God still loves those we hate, and that is rather humbling and forces us to look at ourselves. At the beginning even the worst of us was a baby who could do no wrong. Maybe God understands that the suffering inflicted by evil people are to God more like the reactions of a baby that knows no better. (Just starting to think "aloud" here!) What I do believe is that I am happier than those people doing horrible things to others and so in that regard I am being "rewarded".
I take time every day to feel God's presence. Not to ask for anything, not even asking to feel God's presence! Just freeing my mind and opening myself up. I always feel more Christian at Christmas than I do at Easter. It's the hope and kindness and new beginning I like to focus on, rather than sin.
Not that I'm saying anyone else should feel like this. I think religious variety is God's plan, because we are so different it takes a different way of teaching us to make us understand.
Yes, I do end up being argued with by Christians and atheists alike!! But ultimately, isn't it the way we live rather than exactly what we believe that matters?