How do we know the moral law is still applicable today?

While the ceremonial aspects of the law have been fulfilled in Christ, the moral law, as encapsulated in the Ten Commandments, continues to reflect God's holy character and ethical standards for humanity. It serves to reveal our sinfulness and our inability to attain righteousness on our own, pointing us toward the need for Christ's atoning work. Through the moral law, Christians are guided in their conduct, not as a means to earn salvation, but as a response of gratitude for the grace and mercy they have received through faith.