The idea of sin is an interesting one. It presupposes there is a god to sin against. And that that god has rules. And that somehow, I have broken those rules - whether I have discovered such rules or not.
The idea of sin is purely a faith concept. I believe these things, therefore I understand the concept. But what of those who don't? Can we expect people to understand what cannot be understood outside the faith?
Or is there something bigger in us, outside of faith that can lead us to the same conclusion: that sin exists, and we are sinners?
Despite these questions, if the Bible is true, we are indeed sinners. Not because we have broken God's "rules," but because we have broken God's Rule (that is, His Kingly Rule). we have usurped his power. We have not only taken over dominion over the earth, but everything, and everyone on the earth. Is that the way it's supposed to be?
We have strayed; we have fallen. But the message of the New Testament takes this idea further still. Not only is the existence of God, and God's Rule, and our sin presupposed, but Jesus is also presupposed (or understood) to have the power and authority to forgive such sin. We have reliance on Christ to forgive us for usurping the power of YHWH, the God most high. This is a giant leap of faith. So many presuppositions. This is what Jesus' accusers could not get past. The religious leaders of Jesus' day could not understand how a person could possibly have the power or authority to forgive sin, taking on the role of God, Ruler of All. This is quite a jump to make, and I can honestly say that I would have probably agreed with them.
Nonetheless, if the Bible is true, then this is so. Jesus did and does have the authority to forgiven the sin we have. Again, 'faith' is really the only word in play here. Neither the forgiveness, nor the sin can be proven. They can only be believed in.
And I have faith... that I am a sinner.