And when her days to be delivered were fulfilled. Moses shows that the intestine strife in her womb continued to the time of bringing forth; for it was not by mere accident that Jacob seized his brother by the heel and attempted to get out before him. The Lord testified by this sign that the effect of his election does not immediately appear; but rather that the intervening path was strewed with troubles and conflicts. Therefore Esau's name was allotted to him on account of his asperity; which even from earliest infancy assumed a manly form; but the name Jacob signifies that this giant, vainly striving in his boasted strength, had still been vanquished. [1]

Footnotes

1 - The names of the two brothers was significant of their character. Esau is called Edom, which signifies red, because he was of sanguinary temperament. He is said to have been hairy or shaggy, "sr," from which word the mountainous country he inhabited was called Seir. The name Jacob, "yqv," means to supplant, or trip up the heels. -- Ed

There were twins - תומם thomim, from which comes Thomas, properly interpreted by the word Διδυμος, Didymus, which signifies a twin; so the first person who was called Thomas or Didymus, we may take for granted, had this name from the circumstance of his being a twin.

And when her days to be delivered were fulfilled,.... The nine months were up from the time of her conception; or, as the Targum of Jonathan, when the two hundred and seventy days she went with child were completed:
behold, there were twins in her womb; as was perceived by the midwife; a double mercy was granted, more given than asked for; probably only one child was asked for, but two given.