The cross demonstrates the permanent, immutable nature of God's law. To save us, Jesus did not go around the law. He did not remove it. Rather, he fulfilled it. Taht is because the law is the eternal standard by which we will all be judged, and God is passionate about it. Every jot and tittle of the law must be fulfilled, promised Jesus (Matt. 5:17-20). The cross says, "There will be no lawbreakers in heaven." The cross says, "God is fervent about his law."
Verses such as "Now, by dying to what once bound us, we have been released from the law" (Rom. 7:6) have convinced many that law does not apply to Christians, that in some mysterious way it is no longer relevant or important. In one sense they are right. The law no longer enslaves Christians. We could not keep the law, so Jesus kept it for us. God has released all who put their trust in God's Son from the burden of being perfect law keepers. But the cross reminds us that we will never be released from the law as the standard for judgment.
Jesus did two things on our behalf to fulfill the law. First, he lived a perfect life. He obeyed every jot and tittle of the law so that he could impute that obedience to to unworthy lawbreakers who put their faith in him. Second, on the cross he bore the punishment that lawbreakers deserve. Jesus glorified his Father's passion for his law by both fulfilling it and atoning for its abuse.
William Farley from Outrageous Mercy