" The central point is this: Jesus’ entire approach in the Sermon on the Mount is not only ethical but messianic—i.e., christological and eschatological. Jesus is not an ordinary prophet who says, “Thus says the Lord!” Rather, he speaks in the first person and claims that his teaching fulfills the OT, that he determines who enters the messianic kingdom, that as the Divine Judge he pronounces banishment, that the true heirs of the kingdom will be persecuted for their allegiance to him, and that he alone fully knows the will of his Father. It is methodologically indefensible for Sigal to complain that all such themes are later Christian additions and therefore to focus exclusively on points of halakic interpretation. Jesus’ authority is unique (see comments at 5:21–48), and the crowds recognized it, even if they did not always understand it. This same authority is now to be revealed in powerful, liberating miracles, signs of the kingdom’s advance (chs. 8–9; cf. 11:2–5). "

― D.A. Carson , Matthew (The Expositor's Bible Commentary)