Romans 6:14King James Version (KJV)
14 For sin shall not have dominion over you: for ye are not under the law, but under grace.
Say you were found guilty of murdering someone, and the law of the land sentenced you to death. Can you "work" your way to freedom? No, because you are under the law and it demands your life. The only way you can be free, is if a judge has compassion on you and pardons you. Let's say that happens;
A judge comes along and pardons you. You are now under grace and no longer under the law, which demanded your life. You are free!! Now, do you leave thinking, "I'm free!! I found grace with the judge, I'm free to go and commit more crimes, because I'm now under grace, not under the law!" Of course not.
Any person with an ounce of gratitude would now go and KEEP the law the best they could. And anyway, does the law of the land now become void because you found grace from the judge? No, the law still stands. Do you see this truth with regards to being under grace, not under law?