An excellent discussion of today's (and all the antiphons!) by Father Mark found here.
O Rex Gentium,et desideratus earum,lapisque angularis, qui facis utraque unum: veni, et salva hominem,quem de limo formasti.
O King of the Gentiles or Nations (O Rex Gentium): O King of the Gentiles, Desired of all, you are the cornerstone that binds two into one. Come, and save poor man whom you fashion out of clay.
O Rex Gentium: “O King of all the nations, the only joy of every human heart; O Keystone of the mighty arch of man, come and save the creature you fashioned from the dust.” Isaiah had prophesied, “For a child is born to us, a son is given us; upon his shoulder dominion rests. They name him Wonder-Counselor, God-Hero, Father-Forever, Prince of Peace.” (9:5), and “He shall judge between the nations, and impose terms on many peoples. They shall beat their swords into plowshares and their spears into pruning hooks; one nation shall not raise the sword against another, nor shall they train for war again.” (2:4) .