luke 6:17 And he came down with them, and stood in the plain, and the company of his disciples, and a great multitude of people out of all Judaea and Jerusalem, and from the sea coast of Tyre and Sidon, which came to hear him, and to be healed of their diseases; - Free Bible Online

      17. in the plain--by some rendered "on a level place," that is, a piece of high tableland, by which they understand the same thing, as "on the mountain," where our Lord delivered the sermon recorded by Matthew (Mt 5:1), of which they take this following discourse of Luke to be but an abridged form. But as the sense given in our version is the more accurate, so there are weighty reasons for considering the discourses different. This one contains little more than a fourth of the other; it has woes of its own, as well as the beatitudes common to both; but above all, that of Matthew was plainly delivered a good while before, while this was spoken after the choice of the twelve; and as we know that our Lord delivered some of His weightiest sayings more than once, there is no difficulty in supposing this to be one of His more extended repetitions; nor could anything be more worthy of it.

JFB.