We Christians like to think that the law is a guide for our own behavior but we're quick to forget the other half of what the law says. We've been taught the Ten Commandments for years and would like very much to be able to say that we keep them --at least most of the time. But the commandments are only the first half of the law ...
"Pick up your cross and follow me." That's what Jesus told us to do in. And it's because a believer's cross (denying our own selfish desires) is where the law comes to an end. The law was to lead us to Him for eternal life by showing us our sinful, dead condition. It's a message that He repeats many times, yet we hang on to the law as if it has some additional value for our lives. God has given us His Son Jesus to live in us so that we can be one with Him.
With everything being permissible, isn't it okay to do anything we desire? There aren't any consequences to worry about. So why not just do whatever is pleasing, even at the expense of hurting others? Paul answered this very same question when he saw it coming from the Roman believers.
Even if the law is completed (fulfilled), is it all right to at least use it as a guide to correct our behaviors? Sure! It's up to you if you want to put yourself under the law again. But realize that it's not consistent with what God states in His word. Remember, the law was only to bring you to Christ by showing your sinfulness. That's all the law can do --condemn you!
By faith! ...We're back to the picture of picking up our cross. The penalty for each and every one of our sins has been fully paid by Jesus' death. Now God bases His relationship with you and me as His sons whom He accepts perfectly. There is no sin to stand in the way of our relationship with Him. God counts us as righteous because of our faith in Jesus. And there --at our cross, where we submit to Him and let Jesus take over– is where we can begin to understand freedom. Until that point, our relationship with God is founded on fear of punishment for our shortcomings.
There is no mixing of the law with grace. The law relies on what we do for God; grace relies on what God has done for us. Jesus used two parables to describe what happens when we try to mix them.