I know this is late for those preaching from the lectionary, but through my Technorati watch on the tag [tag]lectionary[/tag], I found this post on Bread and Wine. I think the post helps clarify the passage very well.
With reference to God’s laws, I would add that in general what God has told us to do, God’s commands, provide a good way to live in the world. We have the reward of a life of integrity and of reaping what we sow. What part of that also provides us with a basis on which to demand that God give us eternal life? That is grace.