Jeremiah 49:6

He now says the same thing of the children of Ammon, as he said before of the Moabites, that some hope yet remained for them, for God would at length show mercy to that nation. But, as we have said, these promises were but adventitious, because God had chosen but one people to be a Father to them; and the children of Abraham must be viewed as distinct from all other nations. But though God built, as it were, a wall to separate his people from aliens, it was yet his will to give some preludes of his favor, and of the calling of the Gentiles. The Prophet, then, had here a regard to the kingdom of Christ. The promise, no doubt, extended itself to his coming; for he speaks of the calling of the Gentiles, which God deferred until he manifested his own Son to the world. It is the same then, as though the Prophet had said, that God’s mercy would at length be showed to the Ammonites in common with others; that is, when God would gather his Church from the whole world, and unite, in one body, those who were before scattered. Nor is there a doubt but that the Prophet, speaking of the children of Ammon, intended to show what was to be manifested through all parts of the world. And so it is, that on our calling is our salvation founded, for we see that the gospel has not been, without a design, proclaimed to the world; but as God had determined and settled this from the beginning, so we see that Jeremiah was a herald of our adoption. This, then, is the import of what is said. He afterwards passes over to the children of Edom. But I cannot now proceed farther.