Impossible!

When was the last time you were taken by the impossibility of the Gospel? This was the gist of the sermon on Sunday night.
Sarah (of Sarah and Abraham) laughed at God when He told her she was going to bear a child. She was rebuked, but she was smart enough to laugh. She knew how things worked, what was possible, and what wasn't. She laughed in disbelief. I think it would have been too presumptuous on her part to not laugh or give some sort of strange reaction. Yes, she lacked faith, but rightly so. She was rebuked for this lapse of judgement on her part - not damned.
I've been mulling this over in my head and I remember one fateful weekend several years ago when I was confronted by my sin in a very big way. I was shaking practically the whole weekend. I realized the weight of what I had been doing, but I don't remember taking comfort in the saving work of Christ - at least not right away. I was thankful that for the knowledge that I wasn't damned, but beyond that I didn't have overwhelming joy that accompanied the realization of the depth of my depravity - at least night right away.
I've been reflecting on the words (that I can remember) from Sunday night's sermon.
I'm just not sure how much I actually believe in the impossibility of the Gospel.
I am human after all. I want to feel like I deserve such luxurious treatment.