"But where sin increased, grace abounded all the more."
I've always looked at that verse, and viewed grace like a fully-blown balloon. Can't get any bigger, altho in this case, neither can it get any smaller. It's size was a fixture, never growing, never changing.
My sin was like another balloon still being blown. Sometimes the balloon only grew to a small size, whereas other times, it grew to the same size as the other balloon. But then it stopped, because sin just didn't get any worse than that. I always knew that the grace-balloon would always encompass my sin-balloons, since there's no sin so great that God's grace cannot forgive. But I felt that the size of God's grace surely must be "test-able."
But recently I'd was going through a time of real regret over some choices I had made (not externally bad choice necessarily, but internally just as disparaging). I felt like my sin had just been so great, surely God's grace was tested to the max. Then I re-discovered this verse, or rather, I know the Lord led me to it, and the Holy Spirit did His work. And I saw it so totally differently! I had the balloons all wrong! ( I know "balloons" sound kinda cheesy, but it's just the mental picture that comes to mind, so bare with me!)
Grace is like a balloon that just keeps growing and growing. When I sin and symbolically blow air into the sin-balloon, causing it to grow, the grace-balloon grows at an equal rate, too. One puff into sin, one puff into grace...and the thing is, the grace-balloon started out WAY bigger than the sin-balloon in the first place. It's impossible for the sin-balloon to even dream of catching up. There is no sin so great that God's grace and forgiveness doesn't cleanse, just as easily as I scrub a well-soaked frying-pan.
The size of grace isn't a fixture. It's an ever increasing, ever expanding phenomena of God's mercy.