Matthew 5:17-19 ... But verse 20 must be read in context!
Believers often partake in the discussion on matthew 5:17-19. Many think that the word fulfil means exactly that which Jesus just said He was not come to do.
So you have 2 groups, you have those who are for the Law of God, and those who who are against it, and its an everlasting discussion.
But have you ever read verse 20 together with verse 17-19, because its crucial to understand why Jesus said what He did in verse 17-19!
Matthew 5:20
“For I say unto you, That except your righteousness shall exceed the righteousness of the scribes and Pharisees, ye shall in no case enter into the kingdom of heaven.”
Now Jesus stood up against these "false judahites(jews)" many times and rebuked them for having perverted the Law of God with their own man made religious dogmas and rules.
Read all of Matthew 23, where Jesus rebuke this sect of the pharisees, and the reason why he said what he did in Matthew 5:17-19
He also says: - Matthew 23:4
“For they bind heavy burdens and grievous to be borne, and lay them on men's shoulders; but they themselves will not move them with one of their fingers.”
The religious "jews" followed their traditions of the elders (whats known today as the babylonian talmud) and they upheld all their rabbinical teachings above Gods word, and his eternal law.
This is why Jesus said he was come to fulfil the law, and not do away with it.
look up the word in the concordance, fulfill means to "lift up, uphold, confirm" or simply "to do"
Because the sect of the pharisees had twisted Gods words, and laid their heavy burden on mens shoulders!
Jesus therefore taught the people the true way of Gods commandments.
Same like in Acts 15, many christians use as a go to verse to disprove the law of God.
This was the pharisees again with their man made "heavy burdens" of course not the Law of God.
Because God is Holy and Just, He just wants his people to live how it pleases him (which we also should want)
So it was needed for Jesus to straighten up the law of God, which was hijacked by the pharisees