This has to be one of the most profound quotes that I have ever read. It speaks to what has been done (the gospel) and what we are to do (the law). G. C. Berkouwer writes:
"Grace is the essence of theology and gratitude is the essence of ethics."
To me, that statement says it all. It's just perfect! May God help all of us center our theology on Christ and the gospel, and then work, strive, and "do" out of gratitude for what has already been done.