Again, you should read the book of Acts. When Paul says no one can be saved (or, justified) by the Law he is not saying to disobey God or His Law. He is saying you can only be saved in Jesus, which is true. You are not bound to the Law. This does not mean you do not continue keeping the Law. It simply means you are saved.
Consider also, in addition to Acts 21, Acts 25:7-8 NASB - 7 After Paul arrived, the Jews who had come down from Jerusalem stood around him, bringing many and serious charges against him which they could not prove, 8 while Paul said in his own defense, "I have committed no offense either against the Law of the Jews or against the temple or against Caesar."