-- Philippians 4:19
God says to us, "Come, all you who are thirsty, come to the waters; and you who have no money, come, buy and eat! Come, buy wine and milk without money and without cost" (Isaiah 55:1).
The gospel is addressed to those who have no money or good works. It invites us to come and "buy" salvation without money and without cost. But note the invitation to come is addressed to those who have no money -- not to those who don't have enough. Grace is not a matter of God's making up the difference, but of God's providing all the "cost" of salvation through His Son, Jesus Christ.
-- Jerry Bridges, Transforming Grace
On the flip side, you can't "use up" grace either. Just as there are those who think grace makes up the difference, there are those who think their need is so great it causes fear that it is greater than God's love. But as I told the Element folks last night, you will always have everything you need. You cannot exhaust God's supply of grace. There will always be enough.
How great is God's love for us? Though sin increases, grace increases all the more.