It means exactly what it says:
"Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfill. 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."
Clearly rebukes those who claim the Torah is null and void because of some 'new'
covenant, yes? The few Xians who will even acknowledge 'Til all be fulfilled' will say
that all
has been fulfilled, and to that I say, 'then you don't expect any second coming!'
All means all. Either all is done or it's not, you can't have it both ways.
Let's read on:
"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."
Pretty much the same, eh? Let's read on...
"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."
Ah! Here's where things get tricky. How do you out-Jew a Jew? It makes sense to
think this can't be done. However, in Judaism there's this thing called Kavanah (Intent).
Kavanah - Wikipedia
... and what is the Kavanah of the Pharisees, that Yeshua sees?
“Everything they do is done for people to see: They make their phylacteries wide and the tassels on their garments long" (Matt.23:5)
There it is. The lessons of the Sermon on the Mount and all subsequent teachings.
If there is a 'new' covenant, it's not in abandoning what's been given on Mt. Sinai.
It's in how one approaches obedience to Torah and G-d; the sadly lost lesson:
Where is your heart?