We cannot keep the Law without Christ's aid. He Himself says, "Apart from Me you can do nothing" (John 15:5). So, before we keep the Law, our hearts must be born again through faith.
It is clear why we find fault with the adversaries' doctrine about good works rewarded because of God's generosity. The decision is very easy.
First. The adversaries do not even mention faith, that we please God through faith for Christ's sake. Rather, they imagine that good works, worked by the aid of the habit of love, make a righteousness worthy to please God by itself, and also worthy of eternal life. So they have no need of Christ as Mediator. This is to transfer Christ's glory to our works? It means we would please God because of our works, not because of Christ. But this robs Christ of the glory of being the Mediator. He is the Mediator forever, and not merely in the beginning of justification. Paul also says that if one justified in Christ seeks righteousness elsewhere, he affirms that Christ does not fully justify. What the adversaries teach is most silly. They teach that good works merit grace because of God's mercy. They mean that after the beginning of justification, if conscience is terrified (which happens), grace must be sought through a good work, and not through faith in Christ. (paragraphs 194-197)
Condensed from CONCORDIA: THE LUTHERAN CONFESSIONS, copyright 2005,2006 by Concordia Publishing House. Used by permission. All rights reserved. To purchase a copy of CONCORDIA, call 800-325-3040.