Jesus was sinless, which means that he kept the entire Law perfectly, not just the Ten Commandments. All of God's Laws are moral commands and were given to teach us how to walk in His ways. The Ten Commandments were what the Mosaic Covenant was originally intended to be, but that covenant was never made. It was based upon the condition that the people would hear God's voice and obey (Exodus 19:5), but upon hearing God's voice, the people got cold feet and decided that they wanted God to speak to Moses and to listen to him instead, which was less than ideal, but God nevertheless agreed to this different covenant. It was a exactly like someone saving his damsel in distress out of bondage in Egypt, proposing to her, and with her agreeing, but on the day of her wedding deciding that she only wanted to interact with her husband through a mediator, which he nevertheless agreed to out of his love for her, but Moses could not be everywhere, so that quickly led to problems that would not have happened if the people had been listening to God's voice. In lieu of the people being directed by God voice in how to walk in His ways, it then became necessary for Moses to write down those instructions (Deuteronomy 5:22-33).
The ceremonial laws instruct us how to act in accordance with God's holiness, so they can only be done away with if God's eternal holiness is first done away with. Crosses were never used as a means of disposing of laws, but rather what was written on crosses were the violations of the law or the charges against the person being crucified in order to explain why they were being crucified (
Matthew 27:37). This fits perfectly with the concept of the charges against us or the violations of God's Law that we have committed were nailed to Christ's cross and he died in our place to pay the penalty for our sins, but does not fit at all with doing away with God's holy, righteous, and good Law.
To fulfill the law means "to cause God's will (as made known in the Law) to be obeyed as it should be" (NAS 2c) and after Jesus said he came to fulfill the law, this precisely what Jesus proceeded to do six times throughout the rest of Matthew 5. According to Galatians 5:14, anyone who has ever loved their neighbor has fulfilled the entire law, so it is something that countless people have done, which means that it does not refer to something unique that Jesus did, and certainly not to doing away with God's eternal laws. Likewise, Galatians 6:2 says that bearing one another's burdens fulfills the Law of Christ, which refers to obeying it as it should be obeyed, not to doing away with. In Romans 15:18-19, it says that Paul fulfilled the Gospel, which referred to causing the Gentiles to become fully obedient to it in word and in deed, not to doing away with it.
Jesus warned that those who relaxed the least of the laws or taught others to do the same will be called least in the Kingdom, while those who obey the Law and teach others to do the same will be called great in the Kingdom, so this is something we need to take seriously. Heaven and earth are still here and not all has been accomplished, so God's eternal laws are still in effect. There is nothing in the Bible that speaks about completing the Law by perfectly obeying it, there is nothing in Matthew 5 that indicates that Jesus was referring to his death, and nothing that he said about his death that indicates that he would do away with any of God's eternal laws.
According to Deuteronomy 30:11-14, God said that what He commanded was not too difficult for us, but that His Word is near us, in our mouth and in our heart so that we can obey it, and Romans 10:5-8 quotes this passage in regard to what our faith says, so to say that we are not able to keep God's Law is to call Him a liar and to deny what our faith says. In Titus 2:14, it does not say that Jesus gave himself to free us from the Law, but to free us from all Lawlessness and to purify for himself a people who are zealous for doing good works. So Jesus freed us from sin so that we could be free to obey the Law and thereby meet its righteous requirement (Romans 8:3-4). We have not been given the righteousness of God said that we will hide it under a bushel, but so that we will let it shine, which is in accordance with God's instructions for that as given in His Law and in accordance with the example that Christ set for us to follow.
Indeed, the one and only way that there has ever been to become righteous is through faith, and by there same faith we are therefore required to be careful to obey all of God's commands. God's commands were not given to teach how to act like Jews, but to teach His followers how to walk in His ways. It wouldn't make any sense for Gentiles to say that God has given instructions to His followers for how to follow him, and we should become His followers, but should not follow those instructions because they were only given to His followers and not to people like us who were not his followers.
