Genesis 25:23

... it is spelled as "gaayim" i.e."the proud ones". These are Antoninus and Rebbi, for neither radish nor lettuce ceased to be found on their tables during the sunny or rainy season.

And the Lord said to her, Two peoples are in thy womb, and two kingdoms from thy womb shall be separated; and one kingdom shall be stronger than the other, and the elder shall serve the younger, if the children of the younger will keep the commandments of the Law.

TWO NATIONS ARE IN THY WOMB. The intent of this is that He informed her that she should not fear, for the reason that the struggle in her womb is that she is pregnant with twins, this being the customary way among women who are pregnant with twins.
It is possible that He is also saying that since they are destined to be two peoples, hating and warring with each other, at the very beginning of their creation they initiated a quarrel, thus intimating at the situation which will ultimately exist between them. But He assured her that now they will rest, and she will find rest and quiet for herself.

ויאמר ה' לה, G’d’s answer was provided by the prophet.

שני גויים, do not be upset, seeing that the additional pain you experience is due to the fact that you will give birth to twins. This normally accounts for a more difficult pregnancy.

ושני לאומים, kingdoms, as per Psalms 148,11 מלכי ארץ וכל לאומים, “all kings and peoples of the earth.” We know that this interpretation is correct as otherwise the words גויים and לאומים would simply be a needless repetition. The word לאומים therefore refers to nations. Seeing that the prophet had already begun to foretell Rivkah part of the future, he continued further adding:

ורב יעבוד צעיר, that the younger one would in fact be senior to the older one; as a result of this prophecy Rivkah loved Yaakov more than Esau already from birth.

שני גוים בבטנך, this is the reason for the quarrelling you experience inside your womb.

ושני לאמים, they will also be politically different from one another, being separate kingdoms.

ממעיך יפרדו, they will go their different ways after being born, neither of them will die at birth as you fear.

ויאמר ה' לה, by means of the prophet who was either Shem or Avraham.

שני גויים, the word is written with two letters י and a letter ו which is read but does not appear in the text, something which has been explained in the Talmud Avodah Zarah 11 as affording us the opportunity to read it as גיים, or גאים, a reference to both the Roman Emperor Antoninus as well as Rabbi Yehudah Hanassi, who both occupied lofty positions and were so wealthy that vegetables which have a limited season were never absent from their table all year round. The reading of the text (as opposed to the spelling) would represent the plain meaning then, i.e. peoples.

ושני לאומים, in view of this word here, i.e. a second word referring to nations, it is possible that the spelling of the word גיים is parallel to a plural ending as found in the word איים, from אי, “wild beasts.” The problem is that we do not find לאומיים spelled with two letters י anywhere so that we cannot use it as describing the nature of Esau and the Romans descended from him. Our sages in Yevamot 76 view the spelling as teaching that marriage, i.e. weddings in the accepted sense are not legally possible when only one party to such a union is Jewish, i.e. has already converted. The word גיות is also understood in the sense of widowhood during the lifetime of their husbands. (Samuel II 20,3) The prophet told Rivkah that the strange phenomenon she was experiencing in her womb was a sign that two totally different nations would develop from the twins she was about to give birth to. Most children born by the same father and mother will grow up as part of one and the same nation. Not so in the case of Rivkah’s children. The proof that this interpretation was correct was the very fact that they were already quarrelling with one another even before having been born into this world.

ושני לאומים, we have already mentioned several times (21,1) that it is the practice of the Torah when repeating something to use different words to say basically the same thing.

ורב יעבוד צעיר, “and the older one will serve the younger one.” Our author understands the word רב here not as “older, senior,” as do most commentators, but as meaning הרבה, “many, a great number.” Esau himself used the word in that sense when he told his brother Yaakov: יש לי רב, “I have lots,” (Genesis 33,9) The word may mean “lots” in terms of “time;” i.e. Esau would serve Yaakov for a long time.