How do you destroy the prophets? How do you fulfill the prophets? (doesn't make sense) Unless... you understand.
After his resurrection, Jesus explained what he meant in Matthew 5:17.
The reference was to the Books of the Law, and the Books of the Prophets, and the Psalms. (which also contained prophecies to be fulfilled)
Luke 24:44
He said to them, “This is what I told you while I was still with you: Everything must be fulfilled that is written about me in the Law of Moses, the Prophets and the Psalms.”
Here is Thayer's notes on the Greek word pleeroo in question
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": Mat 5:17; cf. Weiss, Das Matthäusevang. as above with, p. 146f (Compare: ἀναπληρόω, ἀνταναπληρόω, προσαναπληρόω, ἐκπληρόω, συμπληρόω.)*
Here is Robertson's citation on the verse and Greek word in His Book , Word Pictures in the New Testament.
I came not to destroy, but to fulfil (ουκ ηλθον καταλυσα αλλα πληρωσα). The verb "destroy" means to "loosen down" as of a house or tent (2Co 5:1). Fulfil is to fill full. This Jesus did to the ceremonial law which pointed to him and the moral law he kept. "He came to fill the law, to reveal the full depth of meaning that it was intended to hold" (McNeile).
And the BDAG citation
Mt 5:17; depending on how one prefers to interpret the context, πληρόω is understood here either as fulfill=do, carry out, or as bring to full expression=show it forth in its true mng., or as fill up=complete
Now shall we consider context? Let's....
If the law were to be fulfilled in the sense of done away with, then the following warning within the same passage is irrelevant.
Matt 5:18 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.
Heaven and earth have not passed away so not one jot or tittle has passed from the law. Because ALL has not been fulfilled
Matt 5:19 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.
THEREFORE whosoever shall break one of the least of these commandments and teach men so so shall be called least in the Kingdom of heaven. Because heaven and earth have not passed away, all has not been fulfilled. So not one jot or tittle from the law has passed.
Matt 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.
If we do and teach men to break one of the least of the commandments we shall be called least in the Kingdom of Heaven because not one jot or tittle has passed from the law because the all has not been fulfilled. Our righteousness had not exceeded the righteousness of the Pharisees. We shall in no case enter into the Kingdom of Heaven.
And then our Lord and Savior proceeds to give a testimony to what least of these commandments he is referring to.
He goes on to quote some of the Ten and also some of the moral laws contained in the Book of the Law.