Lets expand and put it in context
Matthew 5
17 Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfil.
18 For verily I say unto you, Till heaven and earth pass, one jot or one tittle shall in no wise pass from the law, till all be fulfilled.( Jesus fulfilled it)
19 Whosoever therefore shall break one of these least commandments, and shall teach men so, he shall be called the least in the kingdom of heaven: but whosoever shall do and teach them, the same shall be called great in the kingdom of heaven.
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. ( They kept the Sabbath rigorously)
21 Ye have heard that it was said of them of old time, Thou shalt not kill; and whosoever shall kill shall be in danger of the judgmemt.
22But I say unto you, That whosoever is angry with his brother without a cause shall be in danger of the judgment: and whosoever shall say to his brother, Raca, shall be in danger of the council: but whosoever shall say, Thou fool, shall be in danger of hell fire (This is above Law)
What does it mean to fulfill the Law?
Mat 5:17 Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to
fulfil.
G4137
πληρόω
plēroō
play-ro'-o
From G4134; to make replete, that is, (literally) to cram (a net), level up (a hollow), or (figuratively) to furnish (or imbue, diffuse, influence), satisfy, execute (an office), finish (a period or task), verify (or coincide with a prediction), etc.: - accomplish, X after, (be) complete, end, expire, fill (up), fulfil, (be, make) full (come), fully preach, perfect, supply.
So, taken in context with other quotes from Christ, what does it mean to fulfill the Law? Did Christ keep it so we don't have to? Let's apply that to #6. Did Christ keep the sixth Commandment so we don't have to?
Rom 1:29 Being filled with all unrighteousness, fornication, wickedness, covetousness, maliciousness; full of envy, murder, debate, deceit, malignity; whisperers,
Paul calls murder unrighteousness.
1Pe 4:15 But let none of you suffer as a murderer, or as a thief, or as an evildoer, or as a busybody in other men's matters.
Peter says we should not be a murderer (or a thief, or a busybody).
1Jn 3:15 Whosoever hateth his brother is a murderer: and ye know that no murderer hath eternal life abiding in him.
John says a murder does not have eternal life.
So did Christ keep the Law so that we don't have to? or did He do this...
1Pe 2:21 For even hereunto were ye called: because Christ also suffered for us, leaving us an example, that ye should follow his steps: