3 Nephi 15:5

Behold, I am he that gave the law, and I am he which covenanted with my people Israel; therefore, the law in me is fulfilled: for I have come to fulfil the law; therefore, it hath an end.

I am the one who gave the law. I am the one who made promises to my people Israel. So the law is finished in me. I came to complete the law. That’s why it has ended.

I’m the one who gave that law. I’m the one who made the covenant with Israel. So the law is fulfilled in me. I came to fulfill it, so it has reached its end.