"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.
19 Therefore anyone who sets aside one of the least of these commands and teaches others accordingly will be called least in the kingdom of heaven, but whoever practices and teaches these commands will be called great in the kingdom of heaven," (Matthew 5:17-19)
If you are a new Messianic (or an old one for that matter!), the most important thing for you to be able to understand and defend is Yeshua's stated position on the Law in Matthew 5:17-19.
Now, since you are new, don't worry about the Greek source text yet (when you are older you should consult Torah Resource or read McKee's "The New Testament Validates Torah").
For now, let's make it simple.
You should understand three points about this passage and be able to defend each.
(1) In vs. 17, "abolish" and "fulfill" cannot be synonymous. If they were synonymous then the passage would have the absurd reading "I have not come to abolish but to abolish." Thus, logically, Yeshua argues that the Sinaitic Torah continues to be valid;
(2) In vs. 18, Yeshua asserts that Sinaitic Torah continues until the cosmos is obliterated. The last time I checked, we're still here. Thus, the Sinatic Torah continues to be valid;
(3) In vs. 19, Yeshua warns that if a teacher says that the Sinatic Torah is abolished (in any way) that such a teacher will be rebuked as "least in the kingdom".
[P.S. I really had no idea that Judah selected Matthew 5 for his blog post today!]