At this point we have another abrupt transition. This is the third section of the Sermon. The first section is the Beatitudes where the future blessings of the presently deprived are promised. The second section is the sayings that show the responsibilities of those people who are receiving the gospel that will lead to these blessings. This third section moves to an even more immediate presence. The first set begins with the future so far away that it is after this life. The second section moves closer to a more near future during this life. Now we arrive at the present. What effect does the gospel have upon the believers? How will it change their lives, so that they may become the light of the world, so that they may inherit the kingdom of heaven?
For Israel, and for the Nephites who also followed the Mosaic Law, the issue was a transition from the Law of Moses to the Law of Christ. This section explains the gospel as it grows out of the Law of Moses.
The introductory phrase would have had particular relevance in the Old World. In that context, the statement was one of comfort. Jesus had been accused by the Pharisees of not properly following the rules of ritual purity. Thus there would have been serious questions about whether this teacher was going to attempt to destroy the Law that the Pharisees contended that he was breaking. As Jesus begins to explain how his gospel related to the Law of Moses, he comforts his listeners with the assurance that he is not come to destroy it, as was undoubtedly said of him. Nevertheless, he was not come to replicate current teachings about the Law. What he was going to do was “fulfill.” What he meant by “fulfill”is the subject of this section of the Sermon.
Book of Mormon Context: The meaning of these phrases would have been entirely different in the New World than the Old. The Nephite gospel had been preaching the coming of the Atoning Messiah. The very fact that there would be a universal Atonement would forever alter the need for the atonement sacrifices prescribed in the Law. Therefore, the Nephite gospel lived the Law with an eye to a future alteration in the Law.
Alma 25:15-16
15 Yea, and they did keep the law of Moses; for it was expedient that they should keep the law of Moses as yet, for it was not all fulfilled. But notwithstanding the law of Moses, they did look forward to the coming of Christ, considering that the law of Moses was a type of his coming, and believing that they must keep those outward performances until the time that he should be revealed unto them.
16 Now they did not suppose that salvation came by the law of Moses; but the law of Moses did serve to strengthen their faith in Christ; and thus they did retain a hope through faith, unto eternal salvation, relying upon the spirit of prophecy, which spake of those things to come. (see also Jacob 4:5, Jarom 1:11, Mosiah 3:13-14)
Since the Nephites already had an expectation that the coming of the Atoning Messiah would change the nature of their religious practices, for them the words came not as a comfort of a fear, but a declaration of an answer to a question. They were not afraid that he might change the Law, for they knew that it was inevitable that he should. Their interest was in the method, and therefore them impact of these phrases in the New World would have been the emphasis on the fulfillment rather than the promise that the Law wouldn’t be destroyed.