Jamieson, Fausset & Brown

Now if the fall of them--"But if their trespass," or "false step" be the riches of the--Gentile world--as being the occasion of their accession to Christ. and the diminishing of them--that is, the reduction of the true Israel to so small a remnant. the riches of the Gentiles; how much more their fulness!--that is, their full recovery (see on Rom 11:26); that is, "If an event so untoward as Israel's fall was the occasion of such unspeakable good to the Gentile world, of how much greater good may we expect an event so blessed as their full recovery to be productive?"