In Romans chapter 8, Paul says that Christ is necessary because of what the law could not do. Despite the law being holy, just, and good, it is a curse to those under it. The law promised blessing to the righteous - of which there are none. Christ, the only righteous God, has redeemed us from the curse of the law. If we are in Christ, we are no longer under the schoolmaster that was the law. We are at liberty to serve God, made complete in Christ.