Thanks Octavia, I admire that you posted that. So I think you're right about what you first stated as one of the reasons for the law. As for the second, I could be wrong, but I see your second reason as a natural outcome rather than an initial reason (but that's splitting hairs and doesn't really matter).
Here's how I understand it, the laws in OT were meant as instructions on how to worship and how to provide atonement for sins. So in OT times, they sacrificed innocent animals to "cover" their sins. (I don't know why God accepted animal sacrifices, but then again, if I assume the possibility of an all knowing creator then who am I to question why an animal sacrifice was atonement for sin).
Okay back on subject, this leads to your question about what it means that "Jesus filled the law perfectly". Without going too deep, the Bible explains how Jesus was the perfect sacrifice, a sacrifice to cover man's sins (as well as bridge the chasm between man and God but that's another explanation). Now that Christ sacrificed himself, man no longer needs the law for the atonement of sins. In very short summary, the purpose of the OT law was a way for worship and atonement; the work of Christ now provides that thus fulfilling the law. Man's worship and atonement is now based on our faith in Christ's work.
A final note, I know how this all can sound... ridiculous. All this stuff about sacrifice sounds crazy, I understand. I'll admit that I don't understand God's logic behind it at this point. I have different reasons for my faith (that can be another discussion) even if I don't understand all of it.
One final, final note, thank you for asking the questions you did. Answering them made me really think and check my understanding. As a result, I feel I have a better understanding, so thank you. As the Bible says, "steel sharpens steel." Take care Octavia.