Does God love us and save us because we obey him, or do we obey him because he loves and saves us?
It's an ancient question, to which we all know the answer, but I think the following quote is both concise and potent. Perhaps it is so potent because it is so concise.
"The Old Testament is often caricatured as the testament of law. Of course, there is law in the Old Testament. But before there is law, there is God's grace. What precedes the first commandment? An affirmation that Israel has reached Sinai due entirely to the saving grace of God: 'I am the LORD your God, who brought you out of Egypt, out of the land of slavery.'
The law of God presupposes the grace of God."
from The Image of God by Mark Mangano