matthew 5:17-18 "17 “Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them. 18 For truly I tell you, until heaven and earth disappear, not the smallest letter, not the least stroke of a pen, will by any means disappear from the Law until everything is accomplished."
the "law or the prophets" is referring to the old testament as a whole. by saying that he has "not come to abolish them", he is saying, in sync with "not the smallest letter, not the least stroke of a pen, will by any means disappear from the Law", that he is not denying the validity of the Old Testament as a part of the biblical canon or, Bible.
the "but to fulfill them" part is talking about the fulfillment of the prophecy and of the "Law" or old testament as a whole. he fulfilled their moral law by keeping it perfectly and not sinning. he fulfilled the ceramonial law by being all the symbols, etc that the "law" points to, and lastly, he fulfilled the judicial law by keeping it perfectly.
Galations chapter 3 and 4 talks a lot about the law and the fulfillment of it, and yea. so maybe that helps? i dont know how well written that is..