Can one think of or "use" the thrid use of the Law without being taken back to the second? What is the purpose of the Law for the Christian? Is it there to fulfill for fullfilments sake? Or is it to be fulfilled to please God? Has the law been fulfilled by Christ? Is God our Father pleased with us because of the law or because we have been Baptized and made one with Christ and his death?
"For I am not ashamed of the Gospel for it is the power of God unto salvation for all who believe.” (Romans 1:16)
Gracious Mercy Blog 
Sometimes it helps to think of the “functions” of the Law rather than the “use,” since God is the one who truly makes use of the Law as it hits us. No matter what other function the Law may be serving, it will always ultimately condemn because we will be shown that we fail in keeping it (2nd). Christ has fulfilled the Law and taken away its curse, for us. We see the Law (say, the 10 Commandments as we learn it from the Catechism) giving a description of God’s good will is in our interactions with God and our neighbor. As Christians, we do not ignore the Ten Commandments, but neither do we see them with the power to save or change us for the better. Through the working of God’s Spirit, we strive to keep God’s Law, and even more strongly do we throw ourselves on God’s mercy for our breaking of it. God is pleased with us only in Christ. Thank God!