As Christians, are we under the law? This is a common dispute. There are those who still believe that yes, every law in the Old Testament still applies. And there are verses used to do it. Matthew 5:19, for example, says that disobeying the least of the commandments of the law, and teaching men to do likewise, will result in being called least in the Kingdom of Heaven.
That seems pretty cut and dry, right? You disobey the least of the law, you receive the least status in Heaven. Well, as it turns out, this would result in the Apostles being called the least in the Kingdom. Why? Because they taught that we are no longer under the law, and specifically taught that certain laws had passed. Romans 14 is an excellent example, as it teaches that there are no food laws, since each of us stands or falls before God, and that we actually will stand, because God is able to make us stand. Keep in mind also that though it is Paul who is credited with writing Romans, we are also told that all scripture is inspired by God, and so whatever Paul is guilty of writing in the scriptures, God is also guilty of. I can assure you, God will not be called least in Heaven.
So what did Jesus mean? Well, if we extend our reading beyond verse 19, taking into account Matthew 5:17-20, we see a different story. Jesus isn't saying "you're always going to be under the law". He's effectively saying "the law has a greater purpose, and I'm about to accomplish it".
In Jesus' day, there were a lot of corruptions in the Jewish religion. We see this in Matthew 15 (also Mark 7), where the Pharisees confront Jesus because they did not wash their hands before eating. Jesus' response: "Why do you also transgress the commandment of God because of your tradition? For God commanded, saying, ‘Honor your father and your mother’; and, ‘He who curses father or mother, let him be put to death.’ But you say, ‘Whoever says to his father or mother, “Whatever profit you might have received from me is a gift to God”— then he need not honor his father or mother.’ Thus you have made the commandment of God of no effect by your tradition." (v3-6). The Pharisees were literally changing the law to suit their tradition. In other words, they were disobeying commandments, and teaching men to do the same.
And so Jesus says that these laws were important. He didn't come to abolish them, He came to fulfil them, for not a jot or a tittle would pass away until all was accomplished. Therefore we are told that whoever disobeyed the least, and taught men likewise, would be the least in Heaven. And in verse 20, Jesus drops a scarier truth: Unless your righteousness surpasses that of the scribes and the Pharisees, you will never enter the Kingdom of Heaven.
But that's a works based Gospel, right? Thankfully, no. Remember, this is all one passage. Jesus isn't making separate, contradictory statements here, but one big speech. He had come to fulfil the law. When He declared "it is finished", He meant it. Now, our righteousness can surpass that of the scribes and the Pharisees, not because of anything we've done, but because Jesus' righteousness surpassed that of the Pharisees. And what are we told in 2 Corinthians 5:21? "For He made Him who knew no sin to be sin for us, that we might become the righteousness of God in Him."
The law of Moses was never permanent. From Adam to Moses, it did not exist. From Moses to Jesus, it did. But the moment the curtain was torn in two, the law had been fulfilled, and we are now under a new covenant. A covenant in which the just live not by a law concerning outward things, such as food, but by faith, so that we receive the righteousness of God through Christ.