So, perhaps the significance of grace as it relates to works is that, rather than providing a license to sin, it provides a motive for doing good works that doesn't (or at least is not supposed to) involve pride in oneself and one's accomplishments.
Isn't sinning a rebellion against God? No matter what the sin is? So, if you rebel against God you can't get into heaven. You seem to be all for that.
In this new light, could you clarify why you believe OSAS again?
by this post I thin I can safely assume that you were either never Catholic or never understood it fully.
Trust me, confession is not easy. It is a very good deterrant to sin, though!
And the Catholic Church teaches that "presumption" is a mortal sin. Presumption being sinning on purpose with the intention of just asking for forgiveness later. So, by no means is a serious Catholic going to "slide" in his spirituality because of the sacraments, quite the opposite, actually.
I thought "the sin of presumption" was saying that you had assurance of Heaven.
If what you say is true, the church must not be very clear on it. (and no, I was never a Catholic, but then I wasn't actually singling the Church out in that statement either. Any works religion suffers that temptation.)
Assurance of heaven has never been a part of the Catholic Church. That started with the beginning of Protestant religions and divisions. No Catholic believes OSAS.
Presumption is committing sin with the full intention of just asking God for forgiveness later.
I know the Catholic Church doesn't believe in assurance. Instead, it says that those who do are guilty of the "sin of presumption". That's the context in which I have heard the term.
And Paul is not arguing that unless you achieve sinless perfection you are not saved. But he does provide a list that is clearly out of bounds for a saved Christian.