Fulfill in the KJV is pleroo in the Greek. In Hebrew, the language in which many scholars now believe and testify that Matthew was originally written, it is the word qum or amad which both mean to confirm, establish, fulfill, or to take one's stand, stand up, arise.
Matthew 5:17 “Don’t misunderstand why I have come. I did not come to abolish the law of Moses or the writings
of the prophets. No, I came to accomplish their purpose."
Or the KJV says:
"Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfill."
In Matthew 5:17, Yeshua said He came to fulfill the law, to PLEROO the Law of God. What does that mean?
In a nutshell: The Greek word PLEROO (pronounced play ro' o) means to fully preach. This means that Yeshua said that He came to fully preach the Law of YHWH GOD... if Yeshua FULLY PREACHED the Law of YHWH GOD, then perhaps we should listen to what our Messiah preached.
Jesus (Yeshua) was stating that the Hebrew Bible should not be set aside, it still held authority. He did not come to destroy, abolish, do away with or ignore the Torah or the Prophets. He said so! He came to fully preach, to satisfy, to consumate, to render perfect the Law of YHWH GOD.
Strong's #4137: pleroo (pronounced play-ro'-o)
from 4134; to make replete, i.e. (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.
Thayer's Greek Lexicon:
2c3) to fulfil, i.e. to cause God' s will (as made known in the law) to be obeyed as it should be, and God' s promises (given through the prophets) to receive fulfilment
Then the other day I ran across this explanation that more appropriately explained what I believe Yeshua was saying to his followers in Matthew 5.
"Many...misinterpret these verses because they believe the law is no longer relevant. However, Jesus said He came to fulfill it, which does not mean it was lacking something but that the coming of the Messiah completed the picture. The law now “existed as God originally intended” (Bivin & Blizzard 1994:113). But to know what Jesus really means with “fulfill” and “destroy”, we must go back to the Hebrew culture. “To destroy the law” meant misinterpreting Scripture, while “fulfilling the law” meant correct interpretation – they were technical terms of rabbinic argumentation. What we therefore see in our passage is that Jesus, having been accused of “destroying”, i.e. misinterpreting, the Tanakh (the Torah and Naviim), gives his counterargument that He is actually “fulfilling”, i.e. correctly interpreting it, and actually establishing the correct interpretation of the Tanakh. Stern goes back to our first interpretation by concluding that these verses “enunciate three ways in which the Torah and the Prophets remain necessary, applicable and in force. The remainder of Chapter 5 gives six specific cases in which Yeshua explains the fuller spiritual meaning of points in the Jewish Law. In fact, this verse states the theme and agenda of the entire Sermon on the Mount, in which Yeshua completes, makes fuller, the understanding of his talmidim concerning the Torah and the Prophets, so that they can more fully express what being God’s people is all about.” (Stern 1999:26)"