The first one emerged reddish, as hairy as a fur coat. (Gen. 25:25)

Rabbi Elazar said [regarding the verse] "The first one emerged…": If you say that Jacob was conceived first from the first drop [of semen, see Rashi] this is not so! After all, the verse states, "The first one emerged," not "The first one to emerge…."

"The first one to emerge" would imply that he was only the first to be born, but not necessarily the first one conceived, whereas "The first one emerged" implies that he was the first one to be conceived.

Now, because Isaac came from the aspect of strict justice [din, or gevura, as per Zohar I p. 90b, 103b], Esau was reddish in appearance.

This is because red is associated with that sefira.

Esau was the scum formed from the dregs of gold….

But if Jacob was the first-born, conceived from the first drop, why would [Esau] have emerged reddish from the second drop?

In other words, since Isaac first reproduced his own quality, gevura, had Jacob been the first-born, he would have inherited those traits].

Instead [we must conclude] that Jacob was conceived from the second drop.

Note that non-identical (dizygotic) twins - like Jacob and Esau - result when two eggs are independently fertilized by two different sperm cells.

That is why he did not come out reddish [like Esau] because [the second] drop was from the attribute of compassion [rachamim, related to the sefira of tiferet], from this aspect [the gevura of Isaac], and that aspect [the chesed of Abraham]. So the drop that conceived Esau was not like the drop that conceived Jacob, for Jacob was complete [since he comprised both chesed and gevura], whereas Esau was not complete.

At the time of conception, Isaac was contemplating the furthest effects of harsh din that are produced from his aspect [gevura] when the radiance of his spiritual profile [partzuf] is engraved in his limbs [i.e. in the limbs, or the outer dimensions, of the partzuf].

Therefore Esau was the scum formed from the dregs of gold.

To refine gold, the gold is melted so that the impurities rise to the surface and form a scum on top of the molten gold. Note that gold is associated with gevura, whereas silver is associated with chesed. In fact, gold dust was used by glass-blowers to turn glass red. Isaac is thus metaphorically compared to gold and Esau to the scum that is refined out of the gold.

Accordingly we learn that a person must contemplate the will of his Master at that time [during intercourse] so that they will bring holy children into the world [See Tanya end chap. 2]. But if you think that Isaac did not think in this way [i.e. contemplate holy thoughts] that is not so. He was indeed contemplating holy matters, but his thoughts were on the furthest effects of harsh judgment. Accordingly, when the first drop was issued, his thoughts were in that exact spiritual place…. But Jacob was more of a first-born than Esau, although not from the effects of the first drop, but because Isaac's will was directed towards the "great and powerful tree" [the sefira of tiferet, also called the Tree of Life], whereas Esau came from his thoughts about the outermost reaches of all….

[Based on Zohar III, p. 55a; translation and commentary by Moshe Miller.First published by Fiftieth Gate Publications and Seminars]